Conductive paste for connecting thermoelectric conversion material

ABSTRACT

The present invention provides an electrically conductive paste for connecting thermoelectric materials, the paste comprising a specific powdery oxide and at least one powdery electrically conductive metal selected from the group consisting of gold, silver, platinum, and alloys containing at least one of these metals. By connecting a thermoelectric material to an electrically conductive substrate with the electrically conductive paste of the invention, a suitable electroconductivity is imparted to the connecting portion of the thermoelectric element. Further, the thermal expansion coefficient of the connecting portion can be made close to that of the thermoelectric material. Therefore, even when high-temperature power generation is repeated, separation at the connecting portion is prevented and a favorable thermoelectric performance can be maintained.

TECHNICAL FIELD

The present invention relates to an electrically conductive paste forconnecting thermoelectric materials, a thermoelectric element obtainedusing the-paste, and a thermoelectric module.

BACKGROUND OF THE INVENTION

In Japan, only 30% of the primary energy supply is used as effectiveenergy, with about 70% being eventually lost to the atmosphere as heat.The heat generated by combustion in industrial plants,garbage-incineration facilities or the like is lost to the atmospherewithout conversion into other energy. In this way, a vast amount ofthermal energy is wastefully discarded, while acquiring only a smallamount of energy by combustion of fossil fuels or other means.

To increase the proportion of energy to be utilized, the thermal energycurrently lost to the atmosphere should be effectively used. For thispurpose, thermoelectric conversion, which directly converts thermalenergy to electrical energy, is an effective means. Such athermoelectric conversion utilizes the Seebeck effect, and is an energyconversion method for generating electricity in which a difference inelectric potential is caused by creating a difference in the temperaturebetween both ends of a thermoelectric material.

In such a method for generating electricity utilizing thermoelectricconversion, i.e., thermoelectric generation, electricity is generatedsimply by setting one end of a thermoelectric material at a locationheated to a high temperature by waste heat, and the other end in theatmosphere (room temperature) and connecting conductive wires to bothends. This method entirely eliminates the need for moving parts such asthe motors or turbines generally required for electric power generation.As a consequence, the method is economical and can be carried outwithout generating gases by combustion. Moreover, the method cancontinuously generate electricity until the thermoelectric material hasdeteriorated. Furthermore, thermoelectric generation enables electricpower generation at a high power density. Therefore, it is possible tomake electric power generators (modules) small and light enough to usethem as mobile power supplies for cellular phones, notebook computers,etc.

Therefore, thermoelectric generation is expected to play a role in theresolution of future energy problems. To realize thermoelectricgeneration, a thermoelectric module comprising thermoelectric materialsthat have both a high thermoelectric conversion efficiency and excellentproperties in terms of heat resistance, chemical durability, etc., willbe required.

CoO₂-based layered oxides such as Ca₃Co₄O₉ have been reported assubstances that achieve excellent thermoelectric performance in air athigh temperatures, and such thermoelectric materials are currently beingdeveloped (see R. Funahashi et al., Jpn. J. Appl. Phys., 39, L1127(2000), for example).

The realization of efficient thermoelectric generation using suchthermoelectric materials requires a thermoelectric element comprising apair of connected p- and n-type thermoelectric materials, and athermoelectric module obtained by integrating thermoelectric elements,i.e., an electric power generator. However, the development ofthermoelectric elements and thermoelectric modules has been delayed sofar as compared to the development of thermoelectric materials.

In particular, the development of a method for connecting thermoelectricmaterials with a low electrical resistance is important for puttingthermoelectric modules into practical use. In the case of thermoelectricgeneration using high-temperature waste heat of 673 K (400° C.) orhigher, thermoelectric materials are connected using, as a binder, apaste containing a noble metal such as silver, gold, or platinum becausea connecting portion formed by soldering is likely to oxidize or meltunder such conditions. However, such noble metal pastes are not suitablewhen oxides are used as substrate materials, thermoelectric material,etc. because there is a large difference in the thermal expansioncoefficient between the oxide and the noble metal contained in thepaste. Thus, repeated high-temperature power generations causeseparation at the connecting portion, resulting in increased internalresistance and lowered mechanical strength. The connecting portiontherebetween also has a problem of a large interface resistance due tocontact between the metal and oxide.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems. Aprincipal object of the invention is to provide a material forconnecting thermoelectric materials which can achieve the connection ofthe thermoelectric material made of oxide with a low electricalresistance and which hardly arises a performance deterioration of athermoelectric module even when repeating high-temperature powergeneration and further to provide a thermoelectric element producedusing such a material for connecting thermoelectric materials.

The present inventors conducted extensive research to achieve the aboveobject, and found that when an electrically conductive paste containinga noble metal powder and a specific complex oxide is used for connectingthermoelectric materials, an optimum electrical conductivity is given tothe connecting portion of the thermoelectric material and the separationat the connecting portion can be prevented even when repeatinghigh-temperature power generation. Thus, a good thermoelectricperformance can be maintained over a long period of time. The presentinvention has been accomplished based on these findings.

More specifically, the present invention provides the followingelectrically conductive pastes for connecting thermoelectric materials,thermoelectric elements, thermoelectric modules, and thermoelectricconversion methods.

Item 1. An electrically conductive paste for connecting thermo electricmaterials comprising:

(i) at least one powdery oxide selected from the group consisting ofcomplex oxides (a) to (d):

(a) a complex oxide represented by the formula Ca_(a)A¹ _(b)Co_(c)A²_(d)O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; A² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10;

(b) a complex oxide represented by the formula Bi_(f)Pb_(g)M¹_(h)Co_(i)M² _(j)O_(k) wherein M¹ is one or more elements selected fromthe group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb,Ca, Sr, Ba, Al, Y, and lanthanoids; M² is one or more elements selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, andTa; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10;

(c) a complex oxide represented by the formula Ln_(m)R¹ _(n)Ni_(p)R²_(q)O_(r) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R¹ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R² is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3;

(d) a complex oxide represented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴_(v)O_(w) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R³ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R⁴ is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5; and 3.6≦r≦4.4; and

(ii) at least one powdery electrically conductive metal selected fromthe group consisting of gold, silver, platinum, and alloys containing atleast one of these metals.

Item 2. The electrically conductive paste for connecting thermoelectricmaterials according to Item 1, wherein the powdery oxide mentioned in(i) above is contained in an amount of 0.5 to 20 parts by weight per 100parts by weight of the powdery electrically conductive metal mentionedin (ii) above.

Item 3. The electrically conductive paste for connecting thermoelectricmaterials according to Item 1, further comprising a glass ingredient anda resin ingredient.

Item 4. An electrically conductive paste for connecting a p-typethermoelectric material comprising:

(i) at least one powdery oxide selected from the group consisting of:

a complex oxide represented by the formula Ca_(a)A¹ _(b)Co_(c)A²_(d)O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; A² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10; and

a complex oxide represented by the formula Bi_(f)Pb_(g)M¹ _(h)Co_(i)M²_(j)O_(k) wherein M¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba,Al, Y, and lanthanoids; M² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10; and

(ii) at least one powdery electrically conductive metal selected fromthe group consisting of gold, silver, platinum, and alloys containing atleast one of these metals.

Item 5. The electrically conductive paste for connecting a p-typethermoelectric material according to Item 4, wherein the powdery oxideis at least one member selected from the group consisting of:

a complex oxide represented by the formula Ca_(a)A¹ _(b)Co₄O_(e) whereinA¹ is one or more elements selected from the group consisting of Na, K,Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, andlanthanoids; 2.2≦a≦3.6; 0≦b≦0.8; and 8≦e≦10; and

a complex oxide represented by the formula Bi_(f)Pb_(g)M¹ _(h)Co₂O_(k)wherein M¹ is one or more elements selected from the group consisting ofSr, Ca, and Ba; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10.

Item 6. The electrically conductive paste for connecting a p-typethermoelectric material according to Item 4, wherein the powdery oxidementioned in (i) above is contained in an amount of 0.5 to 20 parts byweight per 100 parts by weight of the powdery electrically conductivemetal mentioned in (ii) above.

Item 7. The electrically conductive paste for connecting a p-typethermoelectric material according to Item 4, further comprising a glassingredient and a resin ingredient.

Item 8. An electrically conductive paste for connecting an n-typethermoelectric material comprising:

(i) at least one powdery oxide selected from the group consisting of:

a complex oxide represented by the formula Ln_(m)R¹ _(n)Ni_(p)R²_(q)O_(r) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R¹ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R²is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3; and

a complex oxide represented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴_(v)O_(w) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R³ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R⁴is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5; and 3.6≦r≦4.4; and

(ii) at least one powdery electrically conductive metal selected fromthe group consisting of gold, silver, platinum, and alloys containing atleast one of these metals.

Item 9. The electrically conductive paste for connecting an n-typethermoelectric material according to Item 8, wherein the powdery oxideis at least one member selected from the group consisting of:

a complex oxide represented by the formula La_(m)R¹ _(n)NiO_(r) whereinR¹ is one or more elements selected from the group consisting of Na, K,Sr, Ca, and Bi; 0.5≦m≦1.2; 0≦n≦0.5; and 2.7≦r≦3.3; and

a complex oxide represented by the formula (La_(s)R³ _(t))₂NiO_(w)wherein R³ is one or more elements selected from the group consisting ofNa, K, Sr, Ca, and Bi; 0.5≦s≦1.2; 0≦t≦0.5; and 3.6≦w≦4.4.

Item 10. The electrically conductive paste for connecting an n-typethermoelectric material according to Item 8, wherein the powdery oxidementioned in (i) above is contained in an amount of 0.5 to 20 parts byweight per 100 parts by weight of the powdery electrically conductivemetal mentioned in (ii) above.

Item 11. The electrically conductive paste for connecting an n-typethermoelectric material according to Item 8, further comprising a glassingredient and a resin ingredient.

Item 12. A thermoelectric element wherein one end of a p-typethermoelectric material and one end of an n-type thermoelectric materialare each connected to an electrically conductive substrate with anelectrically conductive paste,

the p-type thermoelectric material comprising:

a complex oxide represented by the formula Ca_(a)A¹ _(b)Co_(c)A²_(d)O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; A² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10; or a complex oxiderepresented by the formula Bi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k) whereinM¹ is one or more elements selected from the group consisting of Na, K,Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, andlanthanoids; M² is one or more elements selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 1.8≦f≦2.2;0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10;

the n-type thermoelectric material comprising:

a complex oxide represented by the formula Ln_(m)R¹ _(n)Ni_(p)R²_(q)O_(r) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R¹ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R² is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3; or

a complex oxide represented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴_(v)O_(w) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R³ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R⁴ is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5; and 3.6≦r≦4.4;and

the p-type thermoelectric material and the n-type thermoelectricmaterial being each connected to the electrically conductive substratewith the electrically conductive paste of Item 1.

Item 13. A thermoelectric element wherein one end of a p-typethermoelectric material and one end of an n-type thermoelectric materialare each connected to an electrically conductive substrate with anelectrically conductive paste,

the p-type thermoelectric material comprising:

a complex oxide represented by the formula Ca_(a)A¹ _(b)Co_(c)A²_(d)O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; A² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10; or a complex oxiderepresented by the formula Bi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k) whereinM¹ is one or more elements selected from the group consisting of Na, K,Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, andlanthanoids; M² is one or more elements selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 1.8≦f≦2.2;0≦g≦0.4; 1.8 5≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10;

the n-type thermoelectric material comprising:

a complex oxide represented by the formula Ln_(m)R¹ _(n)Ni_(p)R²_(q)O_(r) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R¹ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R²is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦m≦1.2; 0 5≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3; or

a complex oxide represented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴_(v)O_(w) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R³ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R⁴ is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦s≦1.2; 0 5≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5; and 3.6≦r≦4.4;

the electrically conductive paste for connecting the p-typethermoelectric material comprising:

(i) at least one powdery oxide selected from the group consisting of

a complex oxide represented by the formula Ca_(a)A¹ _(b)Co_(c)A²_(d)O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; A² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10; and

a complex oxide represented by the formula Bi_(f)Pb_(g)M¹ _(h)Co_(i)M²_(j)O_(k) wherein M¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba,Al, Y, and lanthanoids; M² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10; and

(ii) at least one powdery electrically conductive metal selected fromthe group consisting of gold, silver, platinum, and alloys containing atleast one of these metals; and

the electrically conductive paste for connecting the n-typethermoelectric material comprising:

(i) at least one powdery oxide selected from the group consisting of

a complex oxide represented by the formula Ln_(m)R¹ _(n)Ni_(p)R²_(q)O_(r) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R¹ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R² is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3; and

a complex oxide represented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴_(v)O_(w) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R³ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R⁴ is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5; and 3.6≦r≦4.4; and

(ii) at least one powdery electrically conductive metal selected fromthe group consisting of gold, silver, platinum, and alloys containing atleast one of these metals.

Item 14. A thermoelectric element wherein one end of a p-typethermoelectric material and one end of an n-type thermoelectric materialare each connected to an electrically conductive substrate with anelectrically conductive paste;

the p-type thermoelectric material comprising a complex oxiderepresented by the formula Ca_(a)A¹ _(b)Co₄O_(e) wherein A¹ is one ormore elements selected from the group consisting of Na, K, Li, Ti, V,Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, and lanthanoids;2.2≦a≦3.6; 0≦b≦0.8; and 8≦e≦10; or a complex oxide represented by theformula Bi_(f)Pb_(g)M¹ _(h)Co₂O_(k) wherein M¹ is one or more elementsselected from the group consisting of Sr, Ca, and Ba; 1.8≦f≦2.2;0≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10;

the n-type thermoelectric material comprising a complex oxiderepresented by the formula La_(m)R¹ _(n)NiO_(r) wherein R¹ is one ormore elements selected from the group consisting of Na, K, Sr, Ca, andBi; 0.5≦m≦1.2; 0≦n≦0.5; and 2.7≦r≦3.3; or a complex oxide represented bythe formula (La_(s)R³ _(t))₂NiO_(w) wherein R³ is one or more elementsselected from the group consisting of Na, K, Sr, Ca, and Bi: 0.5≦s≦1.2;0≦t≦0.5; and 3.6≦w≦4.4;

the electrically conductive paste for connecting the p-typethermoelectric material to the electrically conductive substratecomprising (i) at least one powdery oxide selected from the groupconsisting of a complex oxide represented by the formula Ca_(a)A¹_(b)Co₄O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; 2.2≦a≦3.6; 0≦b≦0.8; and 8≦e≦10; and a complexoxide represented by the formula Bi_(f)Pb_(g)M¹ _(h)Co₂O_(k) wherein M¹is one or more elements selected from the group consisting of Sr, Ca,and Ba; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10; and (ii) at least onepowdery electrically conductive metal selected from the group consistingof gold, silver, platinum, and alloys containing at least one of thesemetals; and

the electrically conductive paste for connecting the n-typethermoelectric material to the electrically conductive substratecomprising (i) at least one powdery oxide selected from the groupconsisting of a complex oxide represented by the formula La_(m)R¹_(n)NiO_(r) wherein R¹ is one or more elements selected from the groupconsisting of Na, K, Sr, Ca, and Bi; 0.5≦m≦1.2; 0≦n≦0.5; and 2.7≦r≦3.3;and a complex oxide represented by the formula (La_(s)R³ _(t))₂NiO_(w)wherein R³ is one or more elements selected from the group consisting ofNa, K, Sr, Ca, and Bi: 0.5≦s≦1.2; 0≦t≦0.5; and 3.6≦w≦4.4; and (ii) atleast one powdery electrically conductive metal selected from the groupconsisting of gold, silver, platinum, and alloys containing at least oneof these metals.

Item 15. A thermoelectric module comprising a plurality of thethermoelectric elements of Item 12, wherein the thermoelectric elementsare connected in series such that an unbonded end portion of the p-typethermoelectric material of one thermoelectric element is connected to anunbonded end portion of the n-type thermoelectric material of anotherthermoelectric element on a substrate.

Item 16. A thermoelectric conversion method comprising positioning oneside of the thermoelectric module of Item 15 at a high-temperatureenvironment and positioning the other side of the module at alow-temperature environment.

Item 17. A thermoelectric module comprising a plurality of thethermoelectric elements of Item 13, wherein the thermoelectric elementsare connected in series such that an unbonded end portion of a p-typethermoelectric material of one thermoelectric element is connected to anunbonded end portion of an n-type thermoelectric material of anotherthermoelectric element on a substrate.

Item 18. A thermoelectric conversion method comprising positioning oneside of the thermoelectric module of Item 17 at a high-temperatureenvironment and positioning the other side of the module at alow-temperature environment.

Hereinafter, the paste for connecting thermoelectric materials of theinvention is described in detail.

Electrically Conductive Paste for Connecting Thermoelectric Materials

The electrically conductive paste for connecting thermoelectricmaterials of the invention comprises a specific powdery oxide and atleast one powdery electrically conductive metal selected from the groupconsisting of gold, silver, platinum, and alloys containing at least oneof these metals as an essential ingredient. These ingredients aredescribed below.

(i) Powdery Electrically Conductive Metal

Usable as the powdery electrically conductive metal are noble metalssuch as silver, gold, and platinum; alloys containing at least one ofsuch noble metals; etc. Usable as such noble metal-containing alloys arealloys containing 30% or more by weight, with about 70% or more byweight being preferable, of noble metal, such as silver, gold, orplatinum. Alloys containing two or more noble metals may be used.

Such a powdery electrically conductive metal can be used singly or incombination of two or more types. The particle size of such a powderyelectrically conductive metal is not limited, but it is preferably suchthat the size of about 80% or more of the metal particles is within therange of about 0.1 μm to about 30 μm.

(ii) Powdery Oxide

Used as a powdery oxide is at least one powdery oxide selected from thegroup consisting of complex oxides (a) to (d):

(a) a complex oxide represented by the formula Ca_(a)A¹ _(b)Co_(c)A²_(d)O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; A² is one or more elements selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta;2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10;

(b) a complex oxide represented by the formula Bi_(f)Pb_(g)M¹_(h)Co_(i)M² _(j)O_(k) wherein M¹ is one or more elements selected fromthe group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb,Ca, Sr, Ba, Al, Y, and lanthanoids; M² is one or more elements selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, andTa; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10;

(c) a complex oxide represented by the formula Ln_(m)R¹ _(n)Ni_(p)R²_(q)O_(r) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R¹ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R² is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3; and

(d) a complex oxide represented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴_(v)O_(w) wherein Ln is one or more elements selected from the groupconsisting of lanthanoids; R³ is one or more elements selected from thegroup consisting of Na, K, Sr, Ca, and Bi; R⁴ is one or more elementsselected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W,Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5; and 3.6≦r≦4.4.

By using the above powdery oxide in combination with at least onepowdery electrically conductive metal selected from the group consistingof gold, silver, platinum, and alloys containing at least one of thesemetals, the thermal expansion coefficient of the connecting portion canbe made close to that of the thermoelectric material, unlike the singleuse of such a powdery electrically conductive metal. Thus, separation atthe connecting portion can be prevented even when high-temperature powergeneration is repeated. Such a powdery oxide has good electricalconductivity and thus can give favorable electrical conductivity to theconnecting portion.

In each formula above, examples of lanthanoids include La, Ce, Pr, Nd,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, etc.

As preferable examples among the above-described complex oxides, thefollowing complex oxides can be mentioned:

(a′) a complex oxide represented by the formula Ca_(a)A¹ _(b)Co₄O_(e)wherein A¹ is one or more elements selected from the group consisting ofNa, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, andlanthanoids; 2.2≦a≦3.6; 0≦b≦0.8; and 8 5≦e≦10;

(b′) a complex oxide represented by the formula Bi_(f)Pb_(g)M¹_(h)CO₂O_(k) wherein M¹ is one or more elements selected from the groupconsisting of Sr, Ca, and Ba; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10;

(c′) a complex oxide represented by the formula La_(m)R¹ _(n)NiO_(r)wherein R¹ is one or more elements selected from the group consisting ofNa, K, Sr, Ca, and Bi; 0.5≦m≦1.2; 0≦n≦0.5; and 2.7≦r≦3.3; and

(d′) a complex oxide represented by the formula (La_(s)R³ _(t))₂NiO_(w)wherein R³ is one or more elements selected from the group consisting ofNa, K, Sr, Ca, and Bi: 0.5≦s≦1.2; 0≦t≦0.5; and 3.6≦w≦4.4.

The complex oxides represented by the above formulae Ca_(a)A¹_(b)CO_(c)A² _(d)O_(e), Bi_(f)Pb_(g)M¹ _(h)Co_(j)M² _(j)O_(k), Ln_(m)R¹_(n)Ni_(p)R² _(q)O_(r), and (Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w) may be inthe form of single crystals or polycrystals.

There are no limitations on the methods for producing such complexoxides insofar as a single crystal or a polycrystal having theabove-mentioned composition can be produced.

Crystal-structured complex oxides having the above-specified compositionmay be produced by known methods. Examples of known methods includesingle crystal-producing methods such as flux methods, zone-meltingmethods, crystal pulling methods, glass annealing methods via glassprecursor, and the like; powder-producing methods such as solid phasereaction methods, sol-gel methods, and the like; film-forming methodssuch as sputtering methods, laser ablation methods, chemical vapordeposition methods, and the like; etc.

As an example, a process for preparing the complex oxide according to asolid phase reaction method among the above methods is described belowin detail.

The above-described complex oxides can be produced by, for example,mixing starting materials in the corresponding proportions to theproportions of the elemental components of the desired complex oxide,and sintering.

The sintering temperature and the sintering time are not limited as longas the desired complex oxide can be obtained. For example, sintering maybe conducted at about 700° C. to about 1200° C. for about 10 to about 40hours. When carbonates, organic compounds, or the like are used asstarting materials, the starting materials are preferably decomposed bycalcination prior to sintering, and then sintered to give the desiredcomplex oxide. For example, when carbonates are used as startingmaterials, they may be calcined at about 700° C. to about 900° C. forabout 10 hours, and then sintered under the above-mentioned conditions.Sintering means are not limited, and any means may be used, includingelectric furnaces and gas furnaces. Usually, sintering may be conductedin an oxidizing atmosphere such as in an oxygen stream or air. When thestarting materials contain a sufficient amount of oxygen, sintering in,for example, an inert atmosphere is also possible. The amount of oxygenin the complex oxide to be produced can be controlled by adjusting thepartial pressure of oxygen during sintering, sintering temperature,sintering time, etc. The higher the partial pressure of oxygen is, thehigher the oxygen ratio in the above formulae can be. For thepreparation of a desired complex oxide according to a solid phasereaction method, it is preferable to prepare a press-molded product froma starting material to sinter the molded product so that the solid phasereaction proceeds efficiently. In this case, the sintered productobtained may be crushed to prepare a powdery material with anappropriate particle size.

In the glass annealing method via a glass precursor, starting materialsare first melted and rapidly cooled for solidification. Any meltingconditions can be employed as long as the starting materials can beuniformly melted. For example, when a crucible of alumina is used as avessel for the melting operation, it is desirable to heat the startingmaterials to about 1200° C. to about 1400° C. to prevent contaminationwith the vessel and to inhibit vaporization of the starting materials.The heating time is not limited, and the heating is continued until auniform melt is obtained. The heating time is usually about 30 minutesto about 1 hour. The heating means are not limited, and any heatingmeans can be employed, including electric furnaces, gas furnaces, etc.The melting can be conducted, for example, in an oxygen-containingatmosphere such as air or an oxygen stream adjusted to a flow rate ofabout 300 ml/min or less. In the case of starting materials containing asufficient amount of oxygen, the melting may be conducted in an inertatmosphere.

The rapid cooling conditions are not limited. The cooling may beconducted to the extent that at least the surface of the solidifiedproduct becomes a glassy amorphous layer. For example, the melt can berapidly cooled by allowing the melt to flow over a metal plate andcompressing the melt from above. The cooling rate may be usually about500° C./sec or greater, and preferably 10³° C./sec or greater.

Subsequently, the product solidified by rapid cooling is heat-treated inan oxygen-containing atmosphere, whereby fibrous single crystals of thedesired complex oxide grow from the surface of the solidified product.

The heat treatment temperature may be in the range of about 880° C. toabout 930° C. The heat treatment may be conducted in anoxygen-containing atmosphere such as in air or an oxygen stream. Whenthe heat treatment is effected in an oxygen stream, the stream may beadjusted to a flow rate of, for example, about 300 ml/min or less, aflow rate of 300ml/min or higher is also acceptable. The heat treatmenttime is not limited and can be determined according to the intendeddegree of growth of the single crystal. The heat treatment time isusually about 60 hours to about 1000 hours.

The mixing ratio of the starting materials can be set depending on thechemical composition of the desired complex oxide. More specifically,when a fibrous complex oxide single crystal is formed from the amorphouslayer of the surface of the solidified product, the oxide single crystalthat grows has the composition of the solid phase in phase equilibriumwith the composition of a melt of the amorphous layer, which isconsidered a liquid phase, of the surface part of the solidifiedproduct. Therefore, the mixing ratio of the starting materials can beset based on the relationship of the chemical composition of the solidphase (single crystal) and the chemical composition of the liquid phase(amorphous layer) in phase equilibrium.

The size of the complex oxide single crystal thus obtained variesdepending on the kind of starting materials, composition ratio, heattreatment conditions, and so on. The single crystal maybe fibrous, forexample, having a length of about 10 μm to about 1000 μm, a width ofabout 20 μm to about 200 μm, and a thickness of about 1 μm to about 5μm.

In both the glass annealing method via glass precursor and the solidphase reaction method, the amount of oxygen contained in the obtainedproduct can be controlled according to the flow rate of oxygen duringheating. The higher the flow rate of oxygen is, the greater the amountof oxygen in the product can be. Variation in the amount of oxygen inthe product does not seriously affect the electrical characteristics ofthe complex oxide. The starting materials are not limited as long asthey can produce oxides when heated. Useful starting materials aremetals, oxides, compounds (such as carbonates), etc. Examples of Casources include calcium oxide (CaO), calcium chloride (CaCl₂), calciumcarbonate (CaCO₃), calcium nitrate (Ca (NO₃)₂), calcium hydroxide (Ca(OH)₂), alkoxides such as dimethoxy calcium (Ca (OCH₃)₂), diethoxycalcium (Ca (OC₂H₅)₂), dipropoxy calcium (Ca(OC₃H₇)₂), and the like,etc. Examples of Co sources include cobalt oxide (CoO, Co₂O₃, andCo₃O₄), cobalt chloride (COCl₂), cobalt carbonate (COCO₃), cobaltnitrate (Co(NO₃)₂), cobalt hydroxide (Co(OH)₂), alkoxides such asdipropoxy cobalt (Co(OC₃H₇)₂), and the like, etc. Similarly, examples ofusable sources of other elements are metals, oxides, chlorides,carbonates, nitrates, hydroxides, alkoxides, etc. Compounds containingtwo or more constituent elements of the complex oxide are also usable.

There is no limitation on the particle size of the powder of at lest onecomplex oxide selected from the group consisting of complex oxidesrepresented by the formulae Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e),Bi_(f)Pb_(g)M¹ _(h)CO_(i); M² _(j)O_(k), Ln_(m)R¹ _(n)Ni_(p)R²_(q)O_(r), and (Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w) but it is preferablysuch that the size of about 80% or more of such oxide particles ispreferably 50 μm or smaller, and preferably about 1 μm to about 10 μm.

(iii) Electrically Conductive Paste Composition

The electrically conductive paste for connecting thermoelectricmaterials of the invention comprises (i) at least one powdery complexoxide selected from the group consisting of complex oxides representedby the formulae (a) Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e), wherein A¹, A², a,b, c, d, and e are as above, (b) Bi_(f)Pb_(g)M¹ _(h)Co_(j)M² _(j)O_(k),wherein M¹, M², f, g, h, i, j, and k are as above, (c) Ln_(m)R¹_(n)Ni_(p)R² _(q)O_(r), wherein Ln, R¹, R², m, n, p, q, and r are asabove, and (d) (Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w), wherein Ln, R³, R⁴,s, t, u, v, and w are as above, and (ii) at least one powderyelectrically conductive metal selected from the group consisting ofgold, silver, platinum, and alloys containing at least one of thesemetals.

In general, the electrically conductive paste may further comprise aglass ingredient, resin ingredient, etc., in addition to theabove-described powdery oxide and powdery electrically conductive metal.

Among these, a glass ingredient primarily exhibits bonding strength whenthe paste is applied to a connecting portion and heated. A glassingredient to be mixed in the electrically conductive paste may beselected from glass ingredients which melt and exhibit bonding strengthwhen heated for bonding and which can maintain sufficient bondingstrength without melting when used for thermoelectric generation.

Such a glass ingredient may be suitably selected from glass ingredientsmixed in known electrically conductive pastes. For example, borosilicatebismuth glass, borosilicate lead glass, etc. can be used.

A resin ingredient imparts suitable dispersibility, thixotropy,viscosity characteristic, etc. to the pastes. Examples of resiningredients include ethyl cellulose, hydroxyethyl cellulose, methylcellulose, nitrocellulose, ethyl cellulose derivatives, acryl-basedresins, butyral resins, alkydphenol resins, epoxy resins, wood rosin,etc.

The proportions of each component are not limited, and may be suitablydetermined according to the desired electrical conductivity, thermalexpansion coefficient, bonding strength, viscosity characteristic, etc.

For example, the oxide powder content is preferably about 0.5 to about20 parts by weight, and more preferably about 1 to about 15 parts byweight, per 100 parts by weight of electrically conductive metal powder.

The glass ingredient content may be, for example, about 0.5 to about 10parts by weight, and preferably about 1 to about 7 parts by weight, per100 parts by weight of electrically conductive metal powder, but can beused in amounts outside these ranges.

Similarly, the resin ingredient content is not limited, and may besuitably set such that suitable workability and sufficient adherence canbe demonstrated. For example, the resin ingredient may be contained inan amount of about 0.5 to 20 parts by weight, preferably about 1 to 10parts by weight, and more preferably about 1 to 5 parts by weight, per100 parts by weight of electrically conductive metal powder.

The electrically conductive paste of the invention may comprise anotheroxide powder, if required. The type, amount, etc. of such oxide powdermay be suitably determined in the range where the above-describedeffects are not adversely effected. For example, it is possible to addan n-type thermoelectric material powder to an electrically conductivepaste for connecting p-type thermoelectric materials.

The electrically conductive paste of the invention may further compriseadditives, such as a solvent, plasticizer, lubricant, antioxidant, andviscosity controller contained in known electrically conductive pastes.Examples of solvents include terpineol, butylcarbitol acetate, etc., andthese solvents can be suitably mixed. The amount of such ingredients maybe suitably determined depending on the desired properties. For example,a solvent can be contained in an amount of about 3 to about 30 parts byweight, and preferably about 5 to about 20 parts by weight, per 100parts by weight of electrically conductive metal powder.

The above-described electrically conductive paste for connectingthermoelectric materials can be used for connecting any type ofthermoelectric material, such as a p-type thermoelectric material and ann-type thermoelectric material, to an electrically conductive substrate.By connecting a thermoelectric material to an electrically conductivesubstrate using the paste for connecting thermoelectric materials, asuitable electroconductivity is imparted to the connecting portion ofthe thermoelectric material. Further, even when high-temperature powergeneration is repeated, separation at the connecting portion is notlikely to occur and a favorable thermoelectric performance can bemaintained over a long period of time.

Preferably, a p-type thermoelectric material is connected to anelectrically conductive substrate using as an oxide powder at least onepowdery oxide selected from the group consisting of complex oxidesrepresented by the formulae Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e), wherein A¹,A², a, b, c, d, and e are as above, and Bi_(f)Pb_(g)M¹ _(h)Co_(i)M²_(j)O_(k), wherein M¹, M², f, g, h, i, j, and k are as above. Suchcomplex oxides exhibit p-type thermo electric material properties. Thus,when a paste containing such complex oxide(s) is used for connectingp-type thermoelectric material, favorable electroconductivity can beimparted to the connecting portion while not adversely affecting thethermoelectric properties of the p-type thermoelectric material, andmoreover the thermal expansion coefficient of the connecting portion canbe made close to that of the thermoelectric material.

An n-type thermoelectric material is preferably connected to anelectrically conductive substrate using as an oxide powder at least onepowdery oxide selected from the group consisting of complex oxidesrepresented by the formulae Ln_(m)R¹ _(n)Ni_(p)R² _(q)O_(r), wherein Ln,R¹, R², m, n, p, q, and r are as above, and (Ln_(s)R³ _(t))₂Ni_(u)R⁴_(v)O_(w), wherein Ln, R³, R⁴, s, t, u, and v are as above. Such complexoxides exhibit n-type thermoelectric material properties. Thus, when apaste containing such complex oxide is used for connecting n-typethermoelectric material, favorable electroconductivity can be impartedto the connecting portion while not adversely affecting thethermoelectric properties of the n-type thermoelectric material, andmoreover the thermal expansion coefficient of the connecting portion canbe made close to that of the thermoelectric material.

Thermoelectric Element

The thermoelectric element of the present invention is formed byconnecting one end of p-type thermoelectric material and one end of ann-type thermoelectric material to an electrically conductive substrate.

Used as each of an electrically conductive paste for connecting p-typethermoelectric materials and an electrically conductive paste forconnecting n-type thermoelectric materials is an electrically conductivepaste, comprising:

(i) at least one powdery complex oxide selected from the groupconsisting of complex oxides represented by the formulae:

(a) Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e), wherein A¹, A², a, b, c, d, and eare as above, (b) Bi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k), wherein M¹, M²,f, g, h, i, j, and k are as above,

(c) Ln_(m)R¹ _(n)Ni_(p)R² _(q)O_(r), wherein Ln, R¹, R², m, n, p, q, andr are as above, and

(d) (Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w), wherein Ln, R³, R⁴, s, t, u, andv are as above, and

(ii) at least one powdery electrically conductive metal selected fromthe group consisting of gold, silver, platinum, and alloys containing atleast one of these metals.

The composition of the electrically conductive paste for connectingp-type thermoelectric materials and the composition of the electricallyconductive paste for connecting n-type thermoelectric materials may bethe same or different. In particular, the use of electrically conductivepastes with the same composition can facilitate the application thereof,thereby efficiently producing thermoelectric elements.

When a paste containing a complex oxide with properties as a p-typethermoelectric material is used for connecting a p-type thermoelectricmaterial to an electrically conductive substrate and a paste containinga complex oxide with properties as an n-type thermoelectric material isused for connecting an n-type thermoelectric material to an electricallyconductive substrate, higher-performance thermoelectric elements can beobtained in which the p-type thermoelectric material properties andn-type thermoelectric material properties are less adversely affected ateach connecting portion. In this case, the electrically conductive pastefor connecting p-type thermoelectric materials comprises at least onepowdery complex oxide selected from the group consisting of complexoxides represented by the formulae Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e),wherein A¹, A², a, b, c, d, and e are as above and Bi_(f)Pb_(g)M¹_(h)Co_(i)M² _(j)O_(k), wherein M¹, M², f, g, h, i, j, and k are asabove. The electrically conductive paste for connecting n-typethermoelectric materials comprises at least one powdery complex oxideselected from the group consisting of complex oxides represented by theformulae Ln_(m)R¹ _(n)Ni_(p)R² _(q)O_(r), wherein Ln, R¹, R², m, n, p,q, and r are as above, and (Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w), whereinLn, R³, R⁴, s, t, u, and v are as above.

Accordingly, the pastes for connecting the p-type thermoelectricmaterial and n-type thermoelectric material to the electricallyconductive substrate may be of the same or different composition, andcan be suitably selected considering the production efficiency anddesired performance of a thermoelectric element to be obtained.

There is no limitation on the p-type thermoelectric materials for use inthe thermoelectric element of the invention. However, among the complexoxide powders to be mixed in the electrically conductive paste forconnecting thermoelectric materials of the invention, it is preferableto use, for the p-type thermoelectric material, a complex oxiderepresented by the formula Ca_(a)A¹ _(b)CO_(c)A² _(d)O_(e) wherein A¹ isone or more elements selected from the group consisting of Na, K, Li,Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, and lanthanoids;A² is one or more elements selected from the group consisting of Ti, V,Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5;0≦d≦2; and 8≦e≦10; or a complex oxide represented by the formulaBi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k) wherein M¹ is one or more elementsselected from the group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni,Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, and lanthanoids; M² is one or moreelements selected from the group consisting of Ti, V, Cr, Mn, Fe, Ni,Cu, Mo, W, Nb, and Ta; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2;0≦j≦0.5; and 8≦k≦10. Such thermoelectric materials may be in the form ofsingle crystals, sintered polycrystals, or thin-films, and can beproduced in the same manner as the complex oxide to be mixed in theelectrically conductive paste, such as single crystal-producing methodssuch as flux methods, zone-melting methods, crystal pulling methods,glass annealing methods via a glass precursor, and the like;powder-producing methods such as solid phase reaction methods, sol-gelmethods, and the like; thin film-forming methods such as sputteringmethods, laser ablation methods, chemical vapor deposition methods, andthe like; etc.

The complex oxides represented by the above formulae have a laminatedstructure with alternating rock-salt structure layers and CoO₂ layers,wherein the rock-salt structure layers have the components Ca, Co, and Oin the ratio of Ca₂CoO₃, or the components Bi, M¹, and in the ratio ofBi₂M¹ ₂O₄; and the CoO₂ layers have octahedrons with octahedralcoordination of six O to one Co, the octahedrons being arrangedtwo-dimensionally such that they share one another's sides. In theformer case, some of the Ca in Ca₂CoO₃ is substituted by A¹, and some ofthe Co of this layer and some of the Co of the CoO₂ layer are furthersubstituted by A². In the latter case, some of the Bi is substituted byPb or some of M¹, and some of the Co is substituted by M².

The complex oxides represented by the above formulae exhibit propertiesas p-type thermoelectric materials in that when a temperature differenceis created between both ends of the oxide material, the electricpotential generated by the Seebeck effect is lower at thehigh-temperature side than at the low-temperature side. Morespecifically, the above complex oxides have a Seebeck coefficient of atleast 100 μV/K and an electrical resistivity of not more than about 10mΩcm at temperatures of 100 K (absolute temperature) or higher. TheSeebeck coefficient tends to increase and the electrical resistivitytends to decrease as the temperature rises.

Among the complex oxides for use in the p-type thermoelectric material,preferable examples include complex oxides represented by the formulaCa_(a)A¹ _(b)Co₄O_(e) wherein A¹ is one or more elements selected fromthe group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb,Sr, Ba, Al, Bi, Y, and lanthanoids; 2.2≦a≦3.6; 0≦b≦0.8; and 8≦e≦10; andcomplex oxides represented by the formula Bi_(f)Pb_(g)M¹ _(h)Co₂O_(k)wherein M¹ is one or more elements selected from the group consisting ofSr, Ca, and Ba; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10.

There is no limitation on the n-type thermoelectric materials for use inthe thermoelectric element of the invention. In particular, among thecomplex oxide powders to be mixed in the electrically conductive pastefor connecting thermoelectric materials of the invention, it ispreferable to use, for the n-type thermoelectric material, complexoxides represented by the formula Ln_(m)R¹ _(n)Ni_(p)R² _(q)O_(r)wherein Ln is one or more elements selected from the group consisting oflanthanoids; R¹ is one or more elements selected from the groupconsisting of Na, K, Sr, Ca, and Bi; R² is one or more elements selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, andTa; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3; or complexoxides represented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w)wherein Ln is one or more elements selected from the group consisting oflanthanoids; R³ is one or more elements selected from the groupconsisting of Na, K, Sr, Ca, and Bi; R⁴ is one or more elements selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, andTa; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0 5≦v≦0.5; and 3.6≦w≦4.4. Suchthermoelectric materials may be in the form of sintered polycrystals,single crystals, or thin-films, and can be produced in the same manneras the complex oxide(s) to be mixed in the electrically conductivepaste. Examples of such method include single crystal-producing methodssuch as flux methods, zone-melting methods, crystal pulling methods,glass annealing methods via a glass precursor, and the like;powder-producing methods such as solid phase reaction methods, sol-gelmethods, and the like; thin film-forming methods such as sputteringmethods, laser ablation methods, chemical vapor deposition methods, andthe like; etc.

The former of the above two kinds of complex oxides has aperovskite-type crystal structure, which is generally referred to as anABO₃ structure. The latter of the above two kinds of complex oxides hasa so-called layered perovskite-type crystal structure, which isgenerally referred to as an A₂BO₄ structure. In these complex oxides,some of Ln is substituted by R¹ or R³, and some of Ni is substituted byR² or R⁴.

The complex oxides represented by the above formulae have a negativeSeebeck coefficient and exhibit properties as n-type thermoelectricmaterials in that when a temperature difference between both ends of theoxide material is created, the electric potential generated by theSeebeck effect is higher at the high-temperature side than at thelow-temperature side. More specifically, the above complex oxides have aSeebeck coefficient of about −1 μV/K to −30 μV/K and exhibit lowelectrical resistances at temperatures of 100 K or higher. For example,the complex oxides tend to exhibit an electrical resistivity of not morethan about 10 mΩcm at temperatures of 100 K or higher.

Among the complex oxides to be used as the n-type thermoelectricmaterial, preferable examples of complex oxides include complex oxidesrepresented by the formula La_(m)R¹ _(n)NiO_(r) wherein R¹ is one ormore elements selected from the group consisting of Na, K, Sr, Ca, andBi; 0.5≦m≦1.2; 0≦n≦0.5; and 2.7≦r≦3.3; and complex oxides represented bythe formula (La_(s)R³ _(t))₂NiO_(w) wherein R³ is one or more elementsselected from the group consisting of Na, K, Sr, Ca, and Bi: 0.5≦s≦1.2;0≦t≦0.5; and 3.6≦w≦4.4.

The size, shape, etc., of the p-type thermoelectric material and then-type thermoelectric material used in the thermoelectric element arenot limited. They may be suitably determined according to the size,shape, etc., of the desired thermoelectric module such that the desiredthermoelectric performance is achieved. Examples thereof includerectangular parallelepiped-shaped materials having a width and thicknessof about 1 mm to about 10 mm and a length of about 1 mm to about 20 mm,cylindrical materials having a length of about 1 mm to about 20 mm and adiameter of about 1 to about 10 mm, etc.

Such thermoelectric materials are obtained by molding the oxide powder,which is obtained in the same manner as the above-described method forproducing the oxide powder for connecting thermoelectric materials,heating the molded doxide powder to provide a sintered product, whennecessary, cutting the sintered product to a predetermined shape with adiamond cutter or the like, and shaping the product.

Any sintering methods can be employed insofar a dense sintered productcan be obtained. Examples of such sintering methods include hot-presssintering method, partial melt method, etc. Sintering may be conductedin an oxidizing atmosphere such as in air or in a vacuum atmosphere butis not limited thereto. The sintering temperature is not limited, andfor example, sintering may be conducted at about 800° C. to about 950°C.

Usable as an electrically conductive substrate to which the p-typethermoelectric material and the n-type thermoelectric material are eachconnected are an electrically conductive ceramic substrate, a substratehaving a metal film formed on an insulative ceramics, etc.

Such an electrically conductive ceramics is preferably a material thatdoes not deteriorate in high-temperature air at about 1073 K (absolutetemperature), and that can maintain low electrical resistance over along period of time. For example, a sintered oxide body with a lowelectrical resistivity, such as LaNiO₃, which is an n-typethermoelectric material, etc., can be used.

The insulative ceramics is preferably a material that does not oxidizein high-temperature air at about 1073 K. For example, a substrate formedof an oxide ceramics such as alumina may be used. The metal film formedon the insulative ceramics is not limited insofar as it is not oxidizedin high-temperature air and has low electrical resistance. Such metalfilm maybe formed of, for example, noble metals such as silver, gold,platinum, etc. by the vapor deposition method, etc.

The length, width, thickness, etc., of the electrically conductivesubstrate may be suitably determined according to module size,electrical resistance, etc. In view of the thermal history of thethermoelectric element and the thermoelectric generation module, it ispreferable that the thermal expansion coefficient of the electricallyconductive substrate be close to the thermal expansion coefficient ofthe thermoelectric material. Moreover, in order to efficiently transferheat from a heat source to the high-temperature side of a thermoelectricelement and to efficiently release heat from the low-temperature side,it is desirable to choose a substrate made of material with high thermalconductivity or to make the substrate thin.

FIG. 1 schematically shows a thermoelectric element of the invention inwhich one end of a p-type thermoelectric material and one end of ann-type thermoelectric material are connected to an electricallyconductive substrate.

The pastes for connecting the p-type thermoelectric material and then-type thermoelectric material to the electrically conductive substratemay be the same. Alternatively, the above-mentioned electricallyconductive paste for connecting p-type thermoelectric materials may beused when a p-type thermoelectric material is connected to theelectrically conductive substrate and the above-mentioned electricallyconductive paste for connecting n-type thermoelectric materials maybeused when an n-type thermoelectric material is connected theelectrically conductive substrate. The specific composition of theseelectrically conductive pastes may be determined according to thedesired mechanical strength, contact resistance, etc. of the connectingportion of the thermoelectric element or thermoelectric module. Sincethe thermal expansion coefficient of-a thermoelectric material orelectrically conductive substrate varies with its composition, thecomposition, amount, etc. of complex oxide(s) to be mixed in theelectrically conductive paste may be determined according to thethermoelectric material or electrically conductive substrate used. Inview of the mechanical and electrical properties, etc. of the connectingportion, the electrically conductive pastes may comprise two or moreoxide powders. Considering the reaction between the thermoelectricmaterial and the oxide powder(s) in the electrically conductive paste,it is particularly preferable to use an oxide powder(s) with the sameconstituent elements as those of the thermoelectric material to whichthe paste is applied for connection.

The connection method maybe the same as conventional methods using anoble metal paste. To be specific, each of the p-type thermoelectricmaterial and the n-type thermoelectric material can be connected to theelectrically conductive substrate by applying the electricallyconductive paste for connecting thermoelectric materials to theconnecting portion between the thermoelectric material and theelectrically conductive substrate, and drying and heating theelectrically conductive paste to solidify it.

The amount of paste is not limited, and may be suitably determinedaccording to the specific composition, etc. of the paste to be appliedin such a manner that the thermoelectric material can be connected tothe electrically conductive substrate with sufficient strength. Forexample, the paste is uniformly applied to the connecting portion insuch a manner that the thickness of paste before solidification is about10 μm to 500 μm and the thickness of the paste layer aftersolidification is about 1 μm to 200 μm.

The heating conditions are not limited, and are usually such thatheating is conducted at about 80° C. to about 200° C. to therebyevaporate the organic solvent, and then heating is further conducted atabout 500° C. to about 900° C. for about 5 minutes to about 1 hour tofix glass ingredients. At the time of connection, in order to tightlyconnect the thermoelectric material to the substrate, the electricallyconductive paste may be solidified under pressure.

Thermoelectric Module

The thermoelectric module of the invention comprises a plurality of theabove-described thermoelectric elements, wherein the thermoelectricelements are connected in series such that an unbonded end portion of ap-type thermoelectric material of one thermoelectric element isconnected to an unbonded end portion of an n-type thermoelectricmaterial of another thermoelectric element.

In general, on a substrate, an end portion of the p-type thermoelectricmaterial of one thermoelectric element is connected to an end portion ofthe n-type thermoelectric material of another thermoelectric element byconnecting unbonded end portions of the thermoelectric elements to thesubstrate with a binder.

FIG. 2 schematically shows one embodiment of a thermoelectric module inwhich a plurality of thermoelectric elements are connected on asubstrate to one another using a binder.

The thermoelectric module of FIG. 2 is obtained by placing a pluralityof the above-described thermoelectric elements on a substrate in such amanner that an unbonded end portion of a p-type thermoelectric materialand an unbonded end portion of an n-type thermoelectric material of eachthermoelectric element are in contact with the substrate, and adheringthe plurality of thermoelectric elements to the substrate in such amanner that the p-type thermoelectric material of one thermoelectricelement and the n-type thermoelectric material of another thermoelectricelement are connected in series.

The main purpose of using a substrate for the thermoelectric module isto improve the thermal uniformity and/or mechanical strength and tomaintain electrically insulative properties, etc. The properties of amaterial for the substrate are not limited, and it is preferable to usefor the substrate a material which does not melt and is not damaged athigh temperatures of at least about 675 K, is chemically stable, is anelectrically insulative material, does not react with the thermoelectricmaterials or the binder, and has a favorable thermal conductivity. Byusing a highly thermally conductive substrate, the temperature of thehigh-temperature side of the element can be made close to that of thehigh-temperature heat source, thereby generating a high voltage. Sincethe thermoelectric material used in the invention is an oxide, oxideceramics, such as alumina, etc., are preferable as substrate materialsconsidering thermal expansion, etc.

It is preferable to use binders capable of connecting the thermoelectricelement to the substrate while maintaining low electrical resistance.For example, pastes containing the noble metals, such as gold, silver,and platinum, solders, etc., can be suitably used. Also usable arepastes whose thermal expansion coefficient is made close to that of thethermoelectric material by adding an electrically conductive oxidepowder to a noble-metal containing paste. Such pasts can prevent theseparation at the connecting portion even when high-temperature powergeneration is repeated. It is possible to use an oxide powder to bemixed in the electrically conductive paste for connecting p-typethermoelectric materials or in the electrically conductive paste forconnecting n-type thermoelectric materials.

The number of the thermoelectric elements used in one module is notlimited, and can be suitably determined depending on the requiredelectric power. FIG. 2 schematically shows the structure of a modulecomprising 84 thermoelectric elements. The output of the module isapproximately equivalent to the value obtained by multiplying the outputof each thermoelectric element by the number of the thermoelectricelements used.

The thermoelectric module of the invention can produce a difference inelectrical potential by positioning one side thereof at ahigh-temperature environment and another side thereof at alow-temperature environment. For example, in the module of FIG. 2, thesubstrate is disposed at a high-temperature environment and the otherside is disposed at a low-temperature environment. Note that thepositioning manner of the thermoelectric module of the invention is notlimited to the above, and all that is required is to position one sideat a high-temperature environment and the other side at alow-temperature environment. For example, in the module of FIG. 2, thehigh-temperature environment and the low-temperature environment can bereversed.

As described above, by electrically connecting a thermoelectric materialto an electrically conductive substrate using the electricallyconductive paste of the present invention, a suitableelectroconductivity is imparted to the connecting portion of thethermoelectric material and the thermal expansion coefficient of theconnecting portion can be made close to that of the thermoelectricmaterial. Thus, even when high-temperature power generation is repeated,separation at the connecting portion is prevented and a favorablethermoelectric performance can be maintained.

Accordingly, the present invention can provide a thermoelectric elementwith excellent performance comprising thermoelectric materials with highthermoelectric conversion efficiency as well as excellent thermalstability, chemical durability, etc.

The thermoelectric module containing such thermoelectric elements haveexcellent thermal stability. Therefore, even when the high-temperatureportion is rapidly cooled from high temperatures of about 1000 K to roomtemperature, the module is not damaged and the power generationcharacteristics thereof are not likely to deteriorate.

As described above, since the thermoelectric module of the invention hashigh output power density even in a small size and high thermal shockresistance, the thermoelectric module can achieve thermoelectricgeneration utilizing, as a heat source, high temperature heat of atleast 473 K generated in industrial plants, garbage-incinerationfacilities, thermal power stations, atomic power stations,microturbines, etc. Moreover, the thermoelectric module of the inventioncan be applied to an electrical power source of automobile, in whichtemperatures rapidly change.

Moreover, since the thermoelectric module can also generate electricityfrom heat energy of about 473 K or lower, low-temperature heat of about293 K to about 473 K, such as solar heat, boiling water, bodytemperature, etc. can be utilized as a heat source. Thus, providing asuitable heat source to the thermoelectric module of the inventionallows the application thereof to a power supply which does not requirerecharging for use in portable equipment such as mobile phones, laptopcomputers, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows one embodiment of a thermoelectric elementformed by connecting thermoelectric materials to an electricallyconductive material with an electrically conductive paste.

FIG. 2 schematically shows a thermoelectric module with a plurality ofthermoelectric elements being connected on a substrate.

FIG. 3 schematically shows the thermoelectric element of Example 1.

FIG. 4 is a chart showing the relationship between the open-circuitvoltage (Vo) and the temperature of the substrate (high temperatureportion) of each thermoelectric element of Example 1 and ComparativeExample 1.

FIG. 5 is a chart showing the relationship between the internalresistance (Ro) and the temperature of the substrate (high temperatureportion) of each thermoelectric element of Example 1 and ComparativeExample.

FIG. 6 is a chart showing the relationship between the maximum outputand the temperature of the substrate (high temperature portion) of eachthermoelectric element of Example 1 and Comparative Example.

FIG. 7 is a chart showing power generation characteristics of athermoelectric module containing the thermoelectric elements of Example1.

EXAMPLES

Hereinafter, the present invention is described in more detail withreference to the following Examples.

Example 1

Production of P-Type Thermoelectric Material

A p-type thermoelectric material represented by the formulaCa_(2.7)Bi_(0.3)Co₄O_(9.2) was produced according to the followingmethod.

Initially, calcium carbonate (CaCO₃), bismuth oxide (Bi₂O₃), and cobaltoxide (Co₃O₄) were weighed out in such a manner as to yield a Ca:Bi:Coratio (atomic ratio) of 2.7:0.3:4 and thoroughly mixed. The mixture wasplaced into an alumina crucible and calcined in air at 1073 K(800° C.)for 10 hours. The calcinate was sufficiently mixed using an agate mortarand pestle.

The obtained powder was molded by pressing into a disk-like form with adiameter of 20 mm and thickness of about 2 mm to about 10 mm. The moldedbody was placed on a gold sheet laid on an alumina boat, and sintered ina 300 ml/minute oxygen stream at 1153 k (880° C.) for 20 hours. Thesintered body thus obtained was crushed using an agate mortar andpestle.

The powder thus obtained was molded by pressing into a plate-like formwith each side being 30 mm and a thickness of 5 mm, followed byhot-press sintering at 1123 K (850° C.) in air under uniaxial pressureof 10 MPa for 20 hours. The hot-pressed sintered body was cut and formedinto a rectangular parallelepiped which has a surface of 4 mm×4 mmperpendicular to the pressed surface and a length of 5 mm in parallel tothe pressed surface, thereby producing a p-type thermoelectric material.

Production of N-Type Thermoelectric Material

An n-type thermoelectric material represented by the formulaLa_(0.9)Bi_(0.1)NiO_(3.1) was produced according to the followingmethod.

Initially, lanthanum nitrate (La(No₃)₃•6H₂O), bismuth nitrate(Bi(No₃)₃•5H₂O), and nickel nitrate (Ni(No₃)₂•6H₂O) were weighed out insuch a manner as to yield a La:Bi:Ni ratio (atomic ratio) of0.9:0.1:1.0, and completely dissolved in distilled water in a crucibleof alumina, followed by mixing. The obtained aqueous solution wasstirred using a magnetic stirrer to evaporate water for solidification.

The obtained solid was heated at 1073 K (800° C.) in air for 10 hours tothermally decompose the nitrate. The obtained calcinate was mixed usingan agate mortar and pestle.

The obtained powder was molded by pressing into a disk-like form with adiameter of 2 cm and thickness of about 2 mm to about 10 mm. The moldedbody was placed on a platinum sheet laid on an alumina boat, followed bysintering in a 300 ml/minute oxygen stream at 1273 k (1000° C.) for 20hours. The sintered body thus obtained was crushed using an agate mortarand pestle. The powder obtained was again molded by pressing to have thesame dimension as mentioned previously, and sintered under the sameconditions. The sintered body was crushed using an agate mortar andpestle.

The powder thus obtained was molded by pressing into a plate-like formwith each side being 30 mm and a thickness of 5 mm, followed byhot-press sintering at 1173 K (950° C.) in air under uniaxial pressureof 10 MPa for 20 hours. The hot-pressed sintered body was cut and formedinto a rectangular parallelepiped which has a surface of 4 mm×4 mmperpendicular to the pressed surface and a length of 5 mm in parallel tothe pressed surface, thereby producing an n-type thermoelectricmaterial.

Preparation of Electrically Conductive Paste for Connecting P-TypeThermoelectric Materials

In the above-described process for producing a p-type thermoelectricmaterial, the powder obtained by crushing the sintered body obtained bysintering at 1153 K (880° C.) for 20 hours was further crushed in a ballmill using an agate pot and ball for 10 minuets. The observation of theobtained oxide powder with a scanning electron microscope showed thatthe diameter of 80% or more of particles was within the range of 1 μm to10 μm.

This oxide powder was mixed in a commercially-available silver paste(trade name: H-4215, manufactured by Shoei Chemical Inc.), preparing anelectrically conductive paste for connecting p-type thermoelectricmaterials. Used was a silver paste comprising 85% by weight of silverpowder (particle diameter of about 0.1 μm to about 5 μm), 1% by weightof borosilicate bismuth glass, 5% by weight of ethyl cellulose, 4% byweight of terpineol, and 5% by weight of butylcarbitol acetate. Theamount of the oxide powder was 6.25 parts by weight per 100 parts byweight of the silver powder of the silver paste.

Preparation of Electrically Conductive Paste for Connecting N-TypeThermoelectric Materials

In the above-described process for producing an n-type thermoelectricmaterial, the powder obtained by conducting twice the process ofsintering at 1273 K (1000° C.) for 20 hours and crushing was furthercrushed in a ball mill using an agate pot and ball for 10 minuets. Theobservation of the obtained oxide powder with a scanning electronmicroscope showed that the particle diameter of 80% or more of particleswas within the range of 1 μm to 10 μm.

This oxide powder was mixed in a commercially-available silver paste,preparing an electrically conductive paste for connecting n-typethermoelectric materials. The type and amount of silver paste were thesame as in the electrically conductive paste for connecting p-typethermoelectric materials.

Production of Thermoelectric Element

A thermoelectric element comprising a pair of a p-type thermoelectricmaterial and an n-type thermoelectric material was produced byconnecting the p-type thermoelectric material and the n-typethermoelectric material to an electrically conductive substrate.

Used as an electrically conductive substrate was a substrate with anelectrically conductive film made from silver paste. The substrate wasobtained by applying the silver paste to a 5 mm×8 mm aluminum platehaving a thickness of 1 mm on the 5 mm×8 mm surface, and then drying thepaste.

The above-described electrically conductive paste for connecting p-typethermoelectric materials and the electrically conductive paste forconnecting n-type thermoelectric materials were applied to the 4 mm×4 mmsurface of the p-type thermoelectric material and the 4 mm×4 mm surfaceof the n-type thermoelectric material, respectively. The p-typethermoelectric material and n-type thermoelectric material were disposedon the alumina substrate in such a manner that the surface of eachthermoelectric material with the electrically conductive paste was incontact with the surface of the alumina substrate whose surface wascoated with the silver film. The resultant was heated at 373 K (100° C.)for about 10 to about 30 minutes, and further heated at 1073 K (800° C.)in air for about 15 minutes to dry the electrically conductive paste forsolidification.

The amount of paste was such that the thickness of the paste beforesolidification was about 50 μm. The thickness of the paste layer aftersolidification was 20 μm.

Subsequently, in order to reinforce the connecting portion of thesubstrate and each thermoelectric material, an insulative ceramic pastecomprising alumina as a main ingredient was applied around eachconnecting portion, and dried, preparing a thermoelectric element. FIG.3 schematically shows the thermoelectric element thus obtained.

Test Results

For the thermoelectric element obtained according to the above-describedmethod, the open-circuit voltage (Vo) and electrical resistance (Ro)were measured under the conditions where the substrate of the elementwas heated to 328 K to 1123 K (55° C. to 850° C.) using an electricfurnace and the opposite end of the element was cooled using a cooler insuch a manner that the temperature difference between the substrate andthe opposite end was 303 K to 773K (30° C. to 500° C.). The term“open-circuit voltage” used herein refers to the voltage producedbetween the low-temperature portion of the p-type thermoelectricmaterial and the low-temperature portion of the n-type thermoelectricmaterial by creating a temperature difference in the thermoelectricelement without connecting external resistance (load).

Separately, as Comparative Example, for thermoelectric element obtainedin the same manner as in Example 1 except that a commercially-availablesilver paste was used by itself with no oxide powder being mixed as eachof the electrically conductive paste for connecting p-typethermoelectric materials and the electrically conductive paste forconnecting n-type thermoelectric materials, the open-circuit voltage Voand electrical resistance Ro were measured in the similar manner asabove.

FIG. 4 is a chart showing the relationship between the open-circuitvoltage Vo and the temperature of the substrate (high temperatureportion). FIG. 4 shows that the open-circuit voltage tends to increasewith the increase in the temperature of the high-temperature portion.This possibly results from the fact that the temperature differencebetween the high-temperature portion and the low-temperature portion canbe enlarged with the increase in the temperature of the high-temperatureportion and moreover the absolute values of an Seebeck coefficient ofthe thermoelectric materials used tend to increase with the rise in thetemperature. Such tendencies were seen in all of Examples describedlater.

When the temperature of the high-temperature portion was adjusted to1073 K to obtain 490 K temperature difference between thehigh-temperature portion and the low-temperature portion, theopen-circuit voltage in Example 1 was 100 mV while that in ComparativeExample was lower, i.e., 70 mV. Such a difference in the open-circuitvoltages possibly results from the fact that, in Comparative Example,some of the thermoelectric materials were separated at the interface ofthe connecting portion because silver paste was used for connecting thethermoelectric materials, which produced a difference in the coefficientof thermal expansion between the silver and the thermoelectric material,and while, in Example 1, the separation at the connecting portion wasnot likely to occur because a specific oxide powder was mixed in theelectrically conductive paste, which made the coefficient of thermalexpansion of the connecting portion close to that of the thermoelectricmaterial.

FIG. 5 is a chart showing the relationship between the internalresistance Ro and the temperature of the substrate (high-temperatureportion). Over the entire temperature range for measurement, theinternal resistance of the element of Example 1 is lower than that ofthe element of Comparative Example. Such a difference possibly resultsfrom the fact that, in the element of Example 1, the separation of thethermoelectric material was prevented and moreover the resistance ofeach interface between the connecting portion and the thermoelectricmaterial was reduced by mixing a specific oxide powder in theelectrically conductive paste.

In general, when an output is obtained by connecting an externalresistance to a power source, the maximum output is obtained when theexternal resistance is the same as the internal resistance of the powersource. In that case, the current Io flowing through the externalresistance is Vo/2Ro, and the obtainable output Pmax (=Imax²Ro) isVo²/4Ro. FIG. 6 is a chart showing the relationship between thetemperature of a high-temperature portion (substrate) and the maximumoutput calculated based on the open-circuit voltage Vo and the internalvoltage Ro. It is found that the element of Example 1 can obtain higheroutputs as compared with the element of Comparative Example.

FIG. 7 is a chart showing the power generation characteristics of athermoelectric module comprising 10 thermoelectric elements obtained inExample 1. Although outputs as estimated from the results of FIG. 6 werenot obtained, it was proved that thermoelectric generation using thismodule can effect the operation of a small motor.

Examples 2 to 94

Thermoelectric elements were produced in the same manner as in Example 1except that the materials represented by the formulae in Tables 1 to 7were used as oxide powder(s) to be mixed in the electrically conductivepastes for connecting p-type thermoelectric materials; oxide powder tobe mixed in the electrically conductive pastes for connecting n-typethermoelectric materials; p-type thermoelectric materials; and n-typethermoelectric materials. The thermoelectric performance of thethermoelectric elements obtained was evaluated. In each Table, theamount of oxide powder to be mixed in the electrically conductive pasteis expressed in parts by weight per 100 parts by weight of silverpowder.

Each Table shows open-circuit voltages measured when the temperatures ofthe high-temperature portion and the low temperature portion were 973 Kand 500 K, respectively, and inner resistances measured when thetemperature of the high-temperature portion was 973K. The thermoelectricelements of all of the Examples exhibited more excellent open-circuitvoltages and inner resistances as compared with those of thermoelectricelements formed by connecting thermoelectric materials of the samecompositions as Examples 2 to 94 with silver paste. TABLE 1 Electricallyconductive paste Powder for p-type material (parts Open-circuitElectrical Examples Thermoelectric material by weight)/Powder for n-typevoltage resistance (No.) p-type material/n-type material Metal material(parts by weight) (mV) (mΩ) 1Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 100 21 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 2 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.7)Bi_(0.3)NiO_(3.3) SilverCa_(2.7)Bi_(0.3)Co₄O_(9.2) (2.0)/ 98 22 La_(0.7)Bi_(0.3)NiO_(3.3) (2.0)3 Ca_(3.3)Bi_(0.5)Co₄O₁₀/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(3.3)Bi_(0.5)Co₄O₁₀ (6.25)/ 100 20 La_(0.9)Bi_(0.1)NiO_(3.1) (6.25) 4Ca_(2.7)Na_(0.3)Co₄O_(8.5)/La_(0.5)NiO_(2.7) SilverCa_(2.7)Na_(0.3)Co₄O_(8.5) (6.25)/ 98 23 La_(0.5)Na_(0.5)NiO_(2.7)(6.25) 5 Ca_(2.7)K_(0.3)Co₄O_(8.4)/La_(0.5)K_(0.5)NiO_(2.8) SilverCa_(2.7)K_(0.3)Co₄O_(8.4) (2.0)/ 95 25 La_(0.5)K_(0.5)NiO_(2.8) (2.0) 6Ca_(2.7)Li_(0.3)Co₄O₈/La_(0.5)Sr_(0.5)NiO_(2.9) SilverCa_(2.7)Bi_(0.3)Co₄O₉ (6.25)/ 90 30 La_(0.5)Sr_(0.5)NiO_(2.9) (6.25) 7Ca_(2.7)Y_(0.3)Co₄O_(9.3)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Y_(0.3)Co₄O_(9.3) (2.0)/ 90 28 La_(0.9)Bi_(0.1)NiO_(3.1) (2.0) 8Ca_(2.7)La_(0.3)Co₄O_(9.5)/LaNiO_(2.9) Silver Ca_(2.7)La_(0.3)Co₄O_(9.5)(6.25)/ 98 22 LaNiO_(2.9) (6.25) 9Ca_(2.7)La_(0.3)Co₄O_(9.5)/La_(1.2)NiO_(3.2) SilverCa_(2.7)La_(0.3)Co₄O_(9.5) (2.0)/ 96 24 La_(1.2)NiO_(3.2) (2.0) 10Ca_(2.7)Ce_(0.3)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Ce_(0.3)Co₄O_(9.4) (6.25)/ 92 25 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 11 Ca_(2.7)Pr_(0.3)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Pr_(0.3)Co₄O_(9.4) (2.0)/ 94 24 La_(0.9)Bi_(0.1)NiO_(3.1) (2.0)12 Ca_(2.7)Nd_(0.3)Co₄O_(9.5)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Nd_(0.3)Co₄O_(9.5) (6.25)/ 97 23 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 13 Ca_(2.7)Sm_(0.3)Co₄O_(9.5)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Sm_(0.3)Co₄O_(9.5) (2.0)/ 98 22 La_(0.9)Bi_(0.1)NiO_(3.1) (2.0)14 Ca_(2.7)Eu_(0.3)Co₄O_(9.3)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Eu_(0.3)Co₄O_(9.3) (6.25)/ 92 29 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 15 Ca_(2.7)Gd_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Gd_(0.3)Co₄O_(9.2) (2.0)/ 95 23 La_(0.9)Bi_(0.1)NiO_(3.1) (2.0)

TABLE 2 Electrically conductive paste Powder for p-type material (partsOpen-circuit Electrical Examples Thermoelectric material byweight)/Powder for n-type voltage resistance (No.) p-typematerial/n-type material Metal material (parts by weight) (mV) (mΩ) 16Ca_(2.7)Dy_(0.3)Co₄O_(9.5)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Dy_(0.3)Co₄O_(9.5) (6.25)/ 91 24 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 17 Ca_(2.7)Ho_(0.3)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Ho_(0.3)Co₄O_(9.4) (2.0)/ 88 29 La_(0.9)Bi_(0.1)NiO₃ (2.0) 18Ca_(2.7)Er_(0.3)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Er_(0.3)Co₄O_(9.4) (6.25)/ 90 28 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 19 Ca_(2.7)Yb_(0.3)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.7)Yb_(0.3)Co₄O_(9.4) (2.0)/ 92 25 La_(0.9)Bi_(0.1)NiO_(3.1) (2.0)20 Ca_(2.2)Sr_(0.8)Co₄O_(8.8)/La_(0.8)Sr_(0.2)NiO_(3.1) SilverCa_(2.2)Sr_(0.8)Co₄O_(8.8) (6.25)/ 97 24 La_(0.8)Sr_(0.2)NiO_(3.1)(6.25) 21 Ca₃Co₄O_(9.2)/La_(0.8)Ca_(0.2)NiO_(3.1) Silver Ca₃Co₄O_(9.2)(2.0)/ 87 30 La_(0.8)Ca_(0.2)NiO_(3.1) (1.0) 22Ca_(3.6)Co₄O_(9.5)/La_(0.8)Ca_(0.2)NiO_(2.9) Silver Ca_(3.6)Co₄O_(9.5)(6.25)/ 85 30 La_(0.8)Ca_(0.2)NiO₃ (1.0) 23Ca_(2.2)Bi_(0.4)Na_(0.4)Co₄O_(9.3)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Bi_(0.4)Na_(0.4)Co₄O_(9.3) (2.0)/ 98 23La_(0.9)Bi_(0.1)NiO_(3.1) (2.0) 24Ca_(2.2)Y_(0.4)Na_(0.4)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Y_(0.4)Na_(0.4)Co₄O_(9.2) (15)/ 92 27 La_(0.9)Bi_(0.1)NiO_(3.1)(15) 25 Ca_(2.2)La_(0.4)Na_(0.4)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO₃ SilverCa_(2.2)La_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 93 28 La_(0.9)Bi_(0.1)NiO₃(6.25) 26 Ca_(2.2)Ce_(0.4)Na_(0.4)Co₄O_(9.5)/La_(0.9)Bi_(0.1)NiO_(3.1)Silver Ca_(2.2)Ce_(0.4)Na_(0.4)Co₄O_(9.5) (15)/ 89 31La_(0.9)Bi_(0.1)NiO_(3.1) (1.0) 27Ca_(2.2)Pr_(0.4)Na_(0.4)Co₄O_(9.3)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Pr_(0.4)Na_(0.4)Co₄O_(9.3) (2.0)/ 89 32La_(0.9)Bi_(0.1)NiO_(3.1) (2.0) 28Ca_(2.2)Nd_(0.4)Na_(0.4)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Nd_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 92 27La_(0.9)Bi_(0.1)NiO_(3.1) (6.25) 29Ca_(2.2)Sm_(0.4)Na_(0.4)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Sm_(0.4)Na_(0.4)Co₄O_(9.4) (2.0)/ 90 28La_(0.9)Bi_(0.1)NiO_(3.1) (2.0) 30Ca_(2.2)Eu_(0.4)Na_(0.4)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Eu_(0.4)Na_(0.4)Co₄O_(9.4) (6.25)/ 88 32La_(0.9)Bi_(0.1)NiO_(3.1) (6.25)

TABLE 3 Electrically conductive paste Powder for p-type material (partsOpen-circuit Electrical Examples Thermoelectric material byweight)/Powder for n-type voltage resistance (No.) p-typematerial/n-type material Metal material (parts by weight) (mV) (mΩ) 31Ca_(2.2)Gd_(0.3)Na_(0.4)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Gd_(0.3)Na_(0.4)Co₄O_(9.4) (2.0)/ 92 26La_(0.9)Bi_(0.1)NiO_(3.1) (1.5) 32Ca_(2.2)Dy_(0.4)Na_(0.4)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Dy_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 90 27La_(0.9)Bi_(0.1)NiO_(3.1) (6.25) 33Ca_(2.2)Ho_(0.1)Na_(0.4)Co₄O_(9.3)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Ho_(0.4)Na_(0.4)Co₄O_(9.3) (2.0)/ 88 29La_(0.9)Bi_(0.1)NiO_(3.1) (1.5) 34Ca_(2.2)Er_(0.4)Na_(0.4)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Er_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 89 32La_(0.9)Bi_(0.1)NiO_(3.1) (6.25) 35Ca_(2.2)Yb_(0.4)Na_(0.4)Co₄O_(9.4)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverCa_(2.2)Yb_(0.4)Na_(0.4)Co₄O_(9.4) (2.0)/ 90 26La_(0.9)Bi_(0.1)NiO_(3.1) (2.0) 36Bi₂Sr₂Co₂O_(9.1)/La_(0.9)Sri_(0.1)NiO_(3.1) Silver Bi₂Sr₂Co₂O_(9.1)(6.25)/ 100 32 La_(0.9)Sri_(0.1)NiO_(3.1) (6.25) 37Bi_(2.2)Sr_(1.8)Co₂O_(8.5)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverBi_(2.2)Sr_(1.8)Co₂O_(8.5) (6.25)/ 98 35 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 38 Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈/La_(0.5)Na_(0.5)NiO_(2.7) SilverBi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈ (6.25)/ 97 33 La_(0.5)Na_(0.5)NiO_(2.7)(6.25) 39 Bi_(1.8)Pb_(0.4)Sr_(2.2)Co₂O_(9.6)/La_(0.5)K_(0.5)NiO_(2.8)Silver Bi_(1.8)Pb_(0.4)Sr_(2.2)Co₂O_(9.6) (6.25)/ 98 35La_(0.5)K_(0.5)NiO_(2.8) (6.25) 40Bi₂Ca₂Co₂O_(9.1)/La_(0.5)Ca_(0.5)NiO_(2.7) Silver Bi₂Ca₂Co₂O_(9.1)(6.25)/ 90 38 La_(0.5)Ca_(0.5)NiO_(2.7) (6.25) 41Bi_(2.2)Ca_(1.8)Co₂O_(9.5)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverBi_(2.2)Ca_(1.8)Co₂O_(9.5) (6.25)/ 92 36 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 42 Bi_(1.8)Pb_(0.2)Ca₂Co₂O_(8.9)/LaNiO_(7.9) SilverBi_(1.8)Pb_(0.2)Ca₂Co₂O_(8.9) (6.25)/ 94 35 LaNiO_(7.9) (6.25) 43Bi_(1.8)Pb_(0.4)Ca_(2.2)Co₂O_(9.4)/LaNiO_(2.9) SilverBi_(1.8)Pb_(0.4)Ca_(2.2)Co₂O_(9.4) (6.25)/ 92 36 LaNiO_(2.9) (6.25) 44Bi₂Ba₂Co₂O₉/La_(0.9)Bi_(0.1)NiO_(3.1) Silver Bi₂Ba₂Co₂O₉ (6.25)/ 80 42La_(0.9)Bo_(0.1)NiO_(3.1) (6.25) 45Bi_(2.2)Ba₂Co₂O₁₀/La_(0.9)Bi_(0.1)NiO_(3.1) Silver Bi_(2.2)Ba₂Co₂O₁₀(6.25)/ 87 40 La_(0.9)Bi_(0.1)NiO_(3.1) (6.25)

TABLE 4 Electrically conductive paste Powder for p-type material (partsOpen-circuit Electrical Examples Thermoelectric material byweight)/Powder for n-type voltage resistance (No.) p-typematerial/n-type material Metal material (parts by weight) (mV) (mΩ) 46Bi_(1.8)Pb_(0.2)Ba₂Co₂O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) SilverBi_(1.8)Pb_(0.2)Ba₂Co₂O_(9.2) (6.25)/ 90 39 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 47 Bi_(1.8)Pb_(0.4)Ba_(2.2)Co₂O_(9.5)/La_(0.9)Bi_(0.1)NiO_(3.1)Silver Bi_(1.8)Pb_(0.4)Ba_(2.2)Co₂O_(9.5) (6.25)/ 90 38La_(0.9)Bi_(0.1)NiO_(3.1) (6.25) 48Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 98 27 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 49 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/(La_(0.7)Bi_(0.3))₂NiO_(4.4) SilverCa_(2.7)Bi_(0.3)Co₄O₉ (2)/ 101 30 (La_(0.7)Bi_(0.3))₂NiO_(4.4) (2) 50Ca_(3.3)Bi_(0.5)Co₄O₁₀/(La_(0.9)Bi_(0.1))₂NiO₄ SilverCa_(3.3)Bi_(0.5)Co₄O₁₀/(La_(0.9)Bi_(0.1))₂NiO₄ 98 32 51Ca_(2.7)Na_(0.3)Co₄O_(8.5)/(La_(0.5)Na_(0.5))₂NiO_(3.8) SilverCa_(2.7)Na_(0.3)Co₄O_(8.5) (6.25)/ 92 32 (La_(0.5)Na_(0.5))₂NiO_(3.8)(6.25) 52 Ca_(2.7)K_(0.3)Co₄O_(8.4)/(La_(0.5)K_(0.5))₂NiO_(3.6) SilverCa_(2.7)K_(0.3)Co₄O_(8.4) (2)/ 93 33 (La_(0.5)K_(0.5))₂NiO_(3.6) (2) 53Ca_(2.7)Li_(0.3)Co₄O₈/(La_(0.5)Sr_(0.5))₂NiO_(3.9) SilverCa_(2.7)Li_(0.3)Co₄O₈ (6.25)/ 90 35 (La_(0.5)Sr_(0.5))₂NiO_(3.9) (6.25)54 Ca_(2.7)Y_(0.3)Co₄O_(9.3)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Y_(0.3)Co₄O_(9.3) (2)/ 92 29 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (2) 55Ca_(2.7)La_(0.3)Co₄O_(9.5)/La₂NiO_(4.1) SilverCa_(2.7)La_(0.3)Co₄O_(9.5) (6.25)/ 97 31 La₂NiO_(4.1) (6.25) 56Ca_(2.7)La_(0.3)Co₄O_(9.5)/La_(2.4)NiO_(4.3) SilverCa_(2.7)La_(0.3)Co₄O_(9.5) (2)/ 95 29 La_(2.4)NiO_(4.3) (2) 57Ca_(2.7)Ce_(0.3)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Ce_(0.3)Co₄O_(9.4) (6.25)/ 92 30 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 58 Ca_(2.7)Pr_(0.3)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Pr_(0.3)Co₄O_(9.4) (2)/ 90 31 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (2)59 Ca_(2.7)Nd_(0.3)Co₄O_(9.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Nd_(0.3)Co₄O_(9.5) (6.25)/ 92 27 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 60 Ca_(2.7)Sm_(0.3)Co₄O_(9.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Sm_(0.3)Co₄O_(9.5) (2)/ 89 31 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (2)

TABLE 5 Electrically conductive paste Powder for p-type material (partsOpen-circuit Electrical Examples Thermoelectric material byweight)/Powder for n-type voltage resistance (No.) p-typematerial/n-type material Metal material (parts by weight) (mV) (mΩ) 61Ca_(2.7)Eu_(0.3)Co₄O_(9.3)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Eu_(0.3)Co₄O_(9.3) (6.25)/ 88 30 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 62 Ca_(2.7)Gd_(0.3)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Gd_(0.3)Co₄O_(9.2) (2)/ 92 29 (La_(0.9)Bi_(0.1))₂NiO_(9.2) (2)63 Ca_(2.7)Dy_(0.3)Co₄O_(9.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Dy_(0.3)Co₄O_(9.5) (6.25)/ 90 31 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 64 Ca_(2.7)Ho_(0.3)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Ho_(0.3)Co₄O_(9.4) (2)/ 87 32 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (2)65 Ca_(2.7)Er_(0.3)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.4) SilverCa_(2.7)Er_(0.3)Co₄O_(9.4) (6.25)/ 87 34 (La_(0.9)Bi_(0.1))₂NiO_(4.4)(6.25) 66 Ca_(2.7)Yb_(0.3)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.7)Yb_(0.3)Co₄O_(9.4) (2)/ 92 27 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (2)67 Ca_(2.2)Sr_(0.8)Co₄O_(8.8)/(La_(0.8)Sr_(0.2))₂NiO_(3.8) SilverCa_(2.2)Sr_(0.8)Co₄O_(8.8) (6.25)/ 98 28 (La_(0.8)Sr_(0.2))₂NiO_(3.8)(6.25) 68 Ca₃Co₄O_(9.2)/(La_(0.8)Ca_(0.2))₂NiO_(3.9) SilverCa₃Co₄O_(9.2) (2)/ 95 30 (La_(0.8)Ca_(0.2))₂NiO_(3.9) (1.5) 69Ca_(3.6)Co₄O_(9.5)/(La_(0.8)Ca_(0.2))₂NiO_(3.9) SilverCa_(3.6)Co₄O_(9.5) (6.25)/ 92 32 (La_(0.8)Ca_(0.2))₂NiO_(3.9) (6.25) 70Ca_(2.2)Bi_(0.4)Na_(0.4)Co₄O_(9.3)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Bi_(0.4)Na_(0.4)Co₄O_(9.3) (2)/ 97 26(La_(0.9)Bi_(0.1))₂NiO_(4.1) (2) 71Ca_(2.2)Y_(0.4)Na_(0.4)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Y_(0.4)Na_(0.4)Co₄O_(9.2) (2)/ 91 29 (La_(0.9)Bi_(0.1))₂NiO₄ (2)72 Ca_(2.2)La_(0.4)Na_(0.4)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1)Silver Ca_(2.2)La_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 90 30(La_(0.9)Bi_(0.1))₂NiO_(4.1) (6.25) 73Ca_(2.2)Ce_(0.4)Na_(0.4)Co₄O_(9.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Ce_(0.4)Na_(0.4)Co₄O_(9.5) (6)/ 90 32 (La_(0.9)Bi_(0.1))₂NiO₄(6.25) 74Ca_(2.2)Pr_(0.4)Na_(0.4)Co₄O_(9.3)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Pr_(0.4)Na_(0.4)Co₄O_(9.3) (2)/ 89 34(La_(0.9)Bi_(0.1))₂NiO_(4.1) (1.5) 75Ca_(2.2)Nd_(0.4)Na_(0.4)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Nd_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 92 29(La_(0.9)Bi_(0.1))₂NiO_(4.1) (6.25)

TABLE 6 Electrically conductive paste Powder for p-type material (partsOpen-circuit Electrical Examples Thermoelectric material byweight)/Powder for n-type voltage resistance (No.) p-typematerial/n-type material Metal material (parts by weight) (mV) (mΩ) 76Ca_(2.2)Sm_(0.4)Na_(0.4)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Sm_(0.4)Na_(0.4)Co₄O_(9.4) (2)/ 93 30(La_(0.9)Bi_(0.1))₂NiO_(4.1) (2) 77Ca_(2.2)Eu_(0.4)Na_(0.4)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Eu_(0.4)Na_(0.4)Co4O_(9.2) (6.25)/ 89 27(La_(0.9)Bi_(0.1))₂NiO_(4.1) (6.25) 78Ca_(2.2)Gd_(0.3)Na_(0.4)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Gd_(0.3)Na_(0.4)Co₄O_(9.4) (2)/ 89 25(La_(0.9)Bi_(0.1))₂NiO_(4.1) (1.5) 79Ca_(2.2)Dy_(0.4)Na_(0.4)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Dy_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 87 30(La_(0.9)Bi_(0.1))₂NiO_(4.1) (6) 80Ca_(2.2)Ho_(0.4)Na_(0.4)Co₄O_(9.3)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Ho_(0.4)Na_(0.4)Co₄O_(9.3) (2)/ 85 32(La_(0.9)Bi_(0.1))₂NiO_(4.1) (1.5) 81Ca_(2.2)Er_(0.4)Na_(0.4)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Er_(0.4)Na_(0.4)Co₄O_(9.2) (6.25)/ 87 30(La_(0.9)Bi_(0.1))₂NiO_(4.1) (6.25) 82Ca_(2.2)Yb_(0.4)Na_(0.4)Co₄O_(9.4)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverCa_(2.2)Yb_(0.4)Na_(0.4)Co₄O_(9.4) (2)/ 88 29(La_(0.9)Bi_(0.1))₂NiO_(4.1) (2) 83Bi₂Sr₂Co₂O_(9.1)/(La_(0.9)Sr_(0.1))₂NiO_(3.9) Silver Bi₂Sr₂Co₂O_(9.1)(6.25)/ 97 37 (La_(0.9)Sr_(0.1))₂NiO_(3.9) (6.25) 84Bi_(2.2)Sr_(1.8)Co₂O_(8.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverBi_(2.2)Sr_(1.8)Co₂O_(8.5) (6.25)/ 95 42 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 85 Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈/(La_(0.5)Na_(0.5))₂NiO_(3.8)Silver Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈ (6.25)/ 94 40(La_(0.5)Na_(0.5))₂NiO_(3.8) (6.25) 86Bi_(1.8)Pb_(0.4)Sr_(2.2)Co₂O_(9.6)/(La_(0.5)K_(0.5))₂NiO_(3.6) SilverBi_(1.8)Pb_(0.4)Sr_(2.2)Co₂O_(9.6) (6.25)/ 92 39(La_(0.5)K_(0.5))₂NiO_(3.6) (6.25) 87Bi₂Ca₂Co₂O_(9.1)/(La_(0.5)Ca_(0.5))₂NiO_(3.7) Silver Bi₂Ca₂Co₂O_(9.1)(6.25)/ 92 43 (La_(0.5)Ca_(0.5))₂NiO_(3.7) (6.25) 88Bi_(2.2)Ca_(1.8)Co₂O_(9.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverBi_(2.2)Ca_(1.8)Co₂O_(9.5) (6.25)/ 89 45 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 89 Bi_(1.8)Pb_(0.2)Ca₂Co_(2O8.9)/La₂NiO_(4.1) SilverBi_(1.8)Pb_(0.2)Ca₂Co₂O_(8.9) (6.25)/ 91 42 La₂NiO_(4.1) (6.25) 90Bi_(1.8)Pb_(0.4)Ca_(2.2)Co₂O_(9.4)/La_(2.4)NiO_(4.3) SilverBi_(1.8)Pb_(0.4)Ca_(2.2)Co₂O_(9.4) (6.25)/ 88 45 La_(2.4)NiO_(4.3)(6.25)

TABLE 7 Electrically conductive paste Powder for p-type material (partsOpen-circuit Electrical Examples Thermoelectric material byweight)/Powder for n-type voltage resistance (No.) p-typematerial/n-type material Metal material (parts by weight) (mV) (mΩ) 91Bi₂Ba₂Co₂O₉/(La_(0.9)Bi_(0.1))₂NiO_(4.1) Silver Bi₂Ba₂Co₂O₉ (6.25)/ 8540 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (6.25) 92Bi_(2.2)Ba₂Co₂O₁₀/(La_(0.9)Bi_(0.1))₂NiO_(4.) Silver Bi_(2.2)Ba₂Co₂O₁₀(6.25)/ 88 43 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (6.25) 93Bi_(1.8)Pb_(0.2)Ba₂Co₂O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverBi_(1.8)Pb_(0.2)Ba₂Co₂O_(9.2) (6.25)/ 90 47 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 94Bi_(1.8)Pb_(0.4)Ba_(2.2)Co₂O_(9.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) SilverBi_(1.8)Pb_(0.4)Ba_(2.2)Co₂O_(9.5) (6.25)/ 90 50(La_(0.9)Bi_(0.1))₂NiO_(4.1) (6.25)

Examples 95 to 106

Oxide powders represented by the formulae shown in Table 8 were used asoxide powders to be mixed in electrically conductive pastes forconnecting p-type thermoelectric materials and electrically conductivepastes for connecting n-type thermoelectric materials. These oxidepowders were mixed in a commercially-available gold paste (trade name:Au-4460, manufactured by Shoei Chemical Inc.), preparing electricallyconductive pastes. The amount of oxide powder in each paste per 100parts by weight of gold is shown in Table 8. The materials representedby the formulae shown in Table 8 were used as p-type thermoelectricmaterials and n-type thermoelectric materials.

Used was a gold paste comprising 85% by weight of gold powder (particlediameter of about 0.1 μm to about 5 μm), 1% by weight of borosilicatebismuth glass, 5% by weight of ethyl cellulose, 4% by weight ofterpineol, and 5% by weight of butylcarbitol acetate. The amount ofoxide powder was 6.25 parts by weight per 100 parts by weight of thesilver powder in each gold paste.

Thermoelectric elements were prepared following the procedure of Example1 except for using the above-mentioned electrically conductive pastesand thermoelectric materials, and thermoelectric performance wasevaluated in the same manner as in Example 1.

Table 8 shows open-circuit voltages measured when the temperatures ofthe high-temperature portion and the low temperature portion were 973Kand 500K, respectively, and inner resistances measured when thetemperature of the high-temperature portion was 973K. The thermoelectricelements of all of the Examples exhibited more excellent open-circuitvoltages and inner resistances as compared with those of thermoelectricelements formed by connecting thermoelectric materials of the samecompositions as Examples 95 to 106 with gold paste. TABLE 8 Electricallyconductive paste Powder for p-type material (parts Open-circuitElectrical Examples Thermoelectric material by weight)/Powder for n-typevoltage resistance (No.) p-type material/n-type material Metal material(parts by weight) (mV) (mΩ) 95Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) GoldCa_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 100 29 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 96 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) GoldCa_(2.7)Bi_(0.3)Co₄O_(9.2) (2.0)/ 97 30 La_(0.9)Bi_(0.1)NiO_(3.1) (2.0)97 Ca_(2.7)Na_(0.3)Co₄O_(8.5)/La_(0.5)Na_(0.5)NiO_(2.7) GoldCa_(2.7)Na_(0.3)Co₄O_(8.5) (6.25)/ 98 29 La_(0.5)Na_(0.5)NiO_(2.7)(6.25) 98 Bi₂Sr₂Co₂O_(9.1)/La_(0.9)Sr_(0.1)NiO_(3.1) GoldBi₂Sr₂Co₂O_(9.1) (6.25)/ 90 36 La_(0.9)Bi_(0.1)NiO₃ (6.25) 99Bi_(2.2)Sr_(1.8)Co₂O_(8.5)/La_(0.9)Bi_(0.1)NiO_(3.1) GoldBi_(2.2)Sr_(1.8)Co₂O_(8.5) (6.25)/ 92 35 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 100 Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈/La_(0.5)Na_(0.5)NiO_(2.7) GoldBi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈ (6.25)/ 92 34 La_(0.5)Na_(0.5)NiO_(2.7)(6.25) 101 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) GoldCa_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 98 32 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 102 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) GoldCa_(2.7)Bi_(0.3)Co₄O_(9.2) (2)/ 97 34 (La_(0.9)Bi_(0.1))₂NiO_(4.1) (2)103 Ca_(2.7)Na_(0.3)Co₄O_(8.5)/(La_(0.5)Na_(0.5))₂NiO_(3.8) GoldCa_(2.7)Na_(0.3)Co₄O_(8.5) (6.25)/ 89 35 (La_(0.5)Na_(0.5))₂NiO_(3.8)(6.25) 104 Bi₂Sr₂Co₂O_(9.1)/(La_(0.9)Sr_(0.1))₂NiO_(3.9) GoldBi₂Sr₂Co₂O_(9.1) (6.25)/ 87 42 (La_(0.9)Sr_(0.1))₂NiO_(3.9) (6.25) 105Bi_(2.2)Sr_(1.8)Co₂O_(8.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) GoldBi_(2.2)Sr_(1.8)Co₂O_(8.5) (6.25)/ 86 40 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 106 Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈/(La_(0.5)Na_(0.5))₂NiO_(3.8)Gold Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈ (6.25)/ 88 39(La_(0.5)Na_(0.5))₂NiO_(3.8) (6.25)

Examples 107 to 121

Oxide powders represented by the formulae shown in Table 9 were used asoxide powders to be mixed in electrically conductive pastes forconnecting p-type thermoelectric materials and electrically conductivepastes for connecting n-type thermoelectric materials. These oxidepowders were mixed in a commercially-available platinum paste (tradename: D-4001, manufactured by Shoei Chemical Inc.), preparingelectrically conductive pastes. The amount of oxide powder in each pasteper 100 parts by weight of platinum is shown in Table 9. The materialsrepresented by the formulae shown in Table 9 were used as p-typethermoelectric materials and n-type thermoelectric materials.

Used was a platinum paste comprising 85% by weight of platinum powder(particle diameter of about 0.1 μm to about 5 μm), 1% by weight ofborosilicate bismuth glass, 5% by weight of ethyl cellulose, 4% byweight of terpineol, and 5% by weight of butylcarbitol acetate. Theamount of oxide powder was 6.25 parts by weight per 100 parts by weightthe silver powder in each platinum paste.

Thermoelectric elements were prepared following the procedure of Example1 except for using the above-mentioned electrically conductive pastesand thermoelectric materials, and thermoelectric performance wasevaluated in the same manner as in Example 1.

Table 9 shows open-circuit voltages measured when the temperatures ofthe high-temperature portion and the low temperature were 973 K and 500K, respectively, and inner resistances measured when the temperature ofthe high-temperature portion was 973K. The thermoelectric elements ofall of the Examples exhibited excellent open-circuit voltage and innerresistance as compared with those of thermoelectric elements formed byconnecting thermoelectric materials of the same compositions as Examples107 to 121 with platinum paste. TABLE 9 Electrically conductive pastePowder for p-type material (parts Open-circuit Electrical ExamplesThermoelectric material by weight)/Powder for n-type voltage resistance(No.) p-type material/n-type material Metal material (parts by weight)(mV) (mΩ) 107 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1)Platinum Ca_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 96 32La_(0.9)Bi_(0.1)NiO_(3.1) (6.25) 108Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) PlatinumCa_(2.7)Bi_(0.3)Co₄O_(9.2) (2.0)/ 87 34 La_(0.9)Bi_(0.1)NiO_(3.1) (2.0)109 Ca_(2.7)Na_(0.3)Co₄O_(8.5)/La_(0.5)Na_(0.5)NiO_(2.7) PlatinumCa_(2.7)Na_(0.3)Co₄O_(8.5) (6.25)/ 85 36 La_(0.5)Na_(0.5)NiO_(2.7)(6.25) 110 Bi₂Sr₂Co₂O_(9.1)/La_(0.9)Sr_(0.1)NiO_(3.1) PlatinumBi₂Sr₂Co₂O_(9.1) (6.25)/ 90 42 La_(0.9)Bi_(0.1)NiO₃ (6.25) 111Bi_(2.2)Sr_(1.8)Co₂O_(8.5)/La_(0.9)Bi_(0.1)NiO_(3.1) PlatinumBi_(2.2)Sr_(1.8)Co₂O_(8.5) (6.25)/ 91 43 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 112 Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈/La_(0.5)Na_(0.5)NiO_(2.7)Platinum Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈ (6.25)/ 89 42La_(0.5)Na_(0.5)NiO_(2.7) (6.25) 113Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) PlatinumCa_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 92 38 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 114 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/(La_(0.9)Bi_(0.1))₂NiO_(4.1)Platinum Ca_(2.7)Bi_(0.3)Co₄O_(9.2) (2)/ 90 35(La_(0.9)Bi_(0.1))₂NiO_(4.1) (2) 115Ca_(2.7)Na_(0.3)Co₄O_(8.5)/(La_(0.5)Na_(0.5))₂NiO_(3.8) PlatinumCa_(2.7)Na_(0.3)Co₄O_(8.5) (6.25)/ 88 36 (La_(0.5)Na_(0.5))₂NiO_(3.8)(6.25) 116 Bi₂Sr₂Co₂O_(9.1)/(La_(0.9)Sr_(0.1))₂NiO_(3.9) PlatinumBi₂Sr₂Co₂O_(9.1) (6.25)/ 87 49 (La_(0.9)Sr_(0.1))₂NiO_(3.9) (6.25) 117Bi_(2.2)Sr_(1.8)Co₂O_(8.5)/(La_(0.9)Bi_(0.1))₂NiO_(4.1) PlatinumBi_(2.2)Sr_(1.8)Co₂O_(8.5) (6.25)/ 84 48 (La_(0.9)Bi_(0.1))₂NiO_(4.1)(6.25) 118 Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈/(La_(0.5)Na_(0.5))₂NiO_(3.8)Platinum Bi_(1.8)Pb_(0.2)Sr_(1.8)Co₂O₈ (6.25)/ 88 50(La_(0.5)Na_(0.5))₂NiO_(3.8) (6.25) 119Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) PlatinumCa_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 97 25 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 120 Ca_(2.7)Bi_(0.3)Co₄O_(9.2)/La_(0.9)Bi_(0.1)NiO_(3.1) PlatinumCa_(2.7)Bi_(0.3)Co₄O_(9.2) (6.25)/ 98 22 La_(0.9)Bi_(0.1)NiO_(3.1)(6.25) 121 Ca_(2.7)Sr₂Co₂O_(9.1)/La_(0.9)Bi_(0.1)NiO_(3.1) PlatinumCa_(2.7)Sr₂Co₂O_(9.1) (6.25)/ 90 34 La_(0.9)Bi_(0.1)NiO_(3.1) (6.25)

1. An electrically conductive paste for connecting thermoelectricmaterials comprising: (i) at least one powdery oxide selected from thegroup consisting of complex oxides (a) to (d): (a) a complex oxiderepresented by the formula Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e) wherein A¹ isone or more elements selected from the group consisting of Na, K, Li,Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, and lanthanoids;A² is one or more elements selected from the group consisting of Ti, V,Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5;0≦d≦2; and 8≦e≦10; (b) a complex oxide represented by the formulaBi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k) wherein M¹ is one or more elementsselected from the group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni,Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, and lanthanoids; M² is one or moreelements selected from the group consisting of Ti, V, Cr, Mn, Fe, Ni,Cu, Mo, W, Nb, and Ta; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2;0≦j≦0.5; and 8≦k≦10; (c) a complex oxide represented by the formulaLn_(m)R¹ _(n)Ni_(p)R² _(q)O_(r) wherein Ln is one or more elementsselected from the group consisting of lanthanoids; R¹ is one or moreelements selected from the group consisting of Na, K, Sr, Ca, and Bi; R²is one or more elements selected from the group consisting of Ti, V, Cr,Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2;0≦q≦0.5; and 2.7≦r≦3.3; (d) a complex oxide represented by the formula(Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w) wherein Ln is one or more elementsselected from the group consisting of lanthanoids; R³ is one or moreelements selected from the group consisting of Na, K, Sr, Ca, and Bi; R⁴is one or more elements selected from the group consisting of Ti, V, Cr,Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2;0≦v≦0.5; and 3.6≦r≦4.4; and (ii) at least one powdery electricallyconductive metal selected from the group consisting of gold, silver,platinum, and alloys containing at least one of these metals.
 2. Theelectrically conductive paste for connecting thermoelectric materialsaccording to claim 1, wherein the powdery oxide mentioned in (i) aboveis contained in an amount of 0.5 to 20 parts by weight per 100 parts byweight of the powdery electrically conductive metal mentioned in (ii)above.
 3. The electrically conductive paste for connectingthermoelectric materials according to claim 1, further comprising aglass ingredient and a resin ingredient.
 4. An electrically conductivepaste for connecting a p-type thermoelectric material comprising: (i) atleast one powdery oxide selected from the group consisting of: a complexoxide represented by the formula Ca_(a)A¹ _(b)CO_(c)A² _(d)O_(e) whereinA¹ is one or more elements selected from the group consisting of Na, K,Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, andlanthanoids; A² is one or more elements selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 2.2≦a≦3.6;0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10; and a complex oxide represented bythe formula Bi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k) wherein M¹ is one ormore elements selected from the group consisting of Na, K, Li, Ti, V,Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, and lanthanoids; M² isone or more elements selected from the group consisting of Ti, V, Cr,Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2;1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10; and (ii) at least one powderyelectrically conductive metal selected from the group consisting ofgold, silver, platinum, and alloys containing at least one of thesemetals.
 5. The electrically conductive paste for connecting a p-typethermoelectric material according to claim 4, wherein the powdery oxideis at least one member selected from the group consisting of: a complexoxide represented by the formula Ca_(a)A¹ _(b)Co₄O_(e) wherein A¹ is oneor more elements selected from the group consisting of Na, K, Li, Ti, V,Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, and lanthanoids;2.2≦a≦3.6; 0 5≦b≦0.8; and 8≦e≦10; and a complex oxide represented by theformula Bi_(f)Pb_(g)M¹ _(h)Co₂O_(k) wherein M¹ is one or more elementsselected from the group consisting of Sr, Ca, and Ba; 1.8≦f≦2.2; 05≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10.
 6. The electrically conductive paste forconnecting a p-type thermoelectric material according to claim 4,wherein the powdery oxide mentioned in (i) above is contained in anamount of 0.5 to 20 parts by weight per 100 parts by weight of thepowdery electrically conductive metal mentioned in (ii) above.
 7. Theelectrically conductive paste for connecting a p-type thermoelectricmaterial according to claim 4, further comprising a glass ingredient anda resin ingredient.
 8. An electrically conductive paste for connectingan n-type thermoelectric material comprising: (i) at least one powderyoxide selected from the group consisting of: a complex oxide representedby the formula Ln_(m)R¹ _(n)Ni_(p)R² _(q)O_(r) wherein Ln is one or moreelements selected from the group consisting of lanthanoids; R¹ is one ormore elements selected from the group consisting of Na, K, Sr, Ca, andBi; R²is one or more elements selected from the group consisting of Ti,V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2;0≦q≦0.5; and 2.7≦r≦3.3; and a complex oxide represented by the formula(Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w) wherein Ln is one or more elementsselected from the group consisting of lanthanoids; R³ is one or moreelements selected from the group consisting of Na, K, Sr, Ca, and Bi;R⁴is one or more elements selected from the group consisting of Ti, V,Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2;0≦v≦0.5; and 3.6≦r≦4.4; and (ii) at least one powdery electricallyconductive metal selected from the group consisting of gold, silver,platinum, and alloys containing at least one of these metals.
 9. Theelectrically conductive paste for connecting an n-type thermoelectricmaterial according to claim 8, wherein the powdery oxide is at least onemember selected from the group consisting of: a complex oxiderepresented by the formula La_(m)R¹ _(n)NiO_(r) wherein R¹ is one ormore elements selected from the group consisting of Na, K, Sr, Ca, andBi; 0.5≦m≦1.2; 0≦n≦0.5; and 2.7≦r≦3.3; and a complex oxide representedby the formula (La_(s)R³ _(t))₂NiO_(w) wherein R³ is one or moreelements selected from the group consisting of Na, K, Sr, Ca, and Bi;0.5≦s≦1.2; 0≦t≦0.5; and 3.6≦w≦4.4.
 10. The electrically conductive pastefor connecting an n-type thermoelectric material according to claim 8,wherein the powdery oxide mentioned in (i) above is contained in anamount of 0.5 to 20 parts by weight per 100 parts by weight of thepowdery electrically conductive metal mentioned in (ii) above.
 11. Theelectrically conductive paste for connecting an n-type thermoelectricmaterial according to claim 8, further comprising a glass ingredient anda resin ingredient.
 12. A thermoelectric element where in one end of ap-type thermoelectric material and one end of an n-type thermoelectricmaterial are each connected to an electrically conductive substrate withan electrically conductive paste, the p-type thermoelectric materialcomprising: a complex oxide represented by the formula Ca_(a)A¹_(b)Co_(c)A² _(d)O_(e) wherein A¹ is one or more elements selected fromthe group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb,Sr, Ba, Al, Bi, Y, and lanthanoids; A² is one or more elements selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, andTa; 2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0≦d≦5 2; and 8≦e≦10; or a complex oxiderepresented by the formula Bi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k) whereinM¹ is one or more elements selected from the group consisting of Na, K,Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, andlanthanoids; M² is one or more elements selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 1.8≦f≦2.2;0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10; the n-typethermoelectric material comprising: a complex oxide represented by theformula Ln_(m)R¹ _(n)Ni_(p)R² _(q)O_(r) wherein Ln is one or moreelements selected from the group consisting of lanthanoids; R¹ is one ormore elements selected from the group consisting of Na, K, Sr, Ca, andBi; R² is one or more elements selected from the group consisting of Ti,V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2;0≦q≦0.5; and 2.7≦r≦3.3; or a complex oxide represented by the formula(Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w) wherein Ln is one or more elementsselected from the group consisting of lanthanoids; R³ is one or moreelements selected from the group consisting of Na, K, Sr, Ca, and Bi;R⁴is one or more elements selected from the group consisting of Ti, V,Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2;0≦v≦0.5; and 3.6≦r≦4.4; and the p-type thermoelectric material and then-type thermoelectric material being each connected to the electricallyconductive substrate with the electrically conductive paste of claim 1.13. A thermoelectric element wherein one end of a p-type thermoelectricmaterial and one end of an n-type thermoelectric material are eachconnected to an electrically conductive substrate with an electricallyconductive paste, the p-type thermoelectric material comprising: acomplex oxide represented by the formula Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e)wherein A¹ is one or more elements selected from the group consisting ofNa, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, andlanthanoids; A² is one or more elements selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 2.2≦a≦3.6;0≦b≦0.8; 2≦c≦4.5; 0≦d≦2; and 8≦e≦10; or a complex oxide represented bythe formula Bi_(f)Pb_(g)M¹ _(h)Co_(i)M² _(j)O_(k) wherein M¹ is one ormore elements selected from the group consisting of Na, K, Li, Ti, V,Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, and lanthanoids; M² isone or more elements selected from the group consisting of Ti, V, Cr,Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2;1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10; the n-type thermoelectric materialcomprising: a complex oxide represented by the formula Ln_(m)R¹_(n)Ni_(p)R² _(q)O_(r) wherein Ln is one or more elements selected fromthe group consisting of lanthanoids; R¹ is one or more elements selectedfrom the group consisting of Na, K, Sr, Ca, and Bi; R² is one or moreelements selected from the group consisting of Ti, V, Cr, Mn, Fe, Ni,Cu, Mo, W, Nb, and Ta; 0.5≦m≦1.2; 0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and2.7≦r≦3.3; or a complex oxide represented by the formula (Ln_(s)R³_(t))₂Ni_(u)R⁴ _(v)O_(w) wherein Ln is one or more elements selectedfrom the group consisting of lanthanoids; R³ is one or more elementsselected from the group consisting of Na, K, Sr, Ca, and Bi; R⁴ is oneor more elements selected from the group consisting of Ti, V, Cr, Mn,Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5;and 3.6≦r≦4.4; the electrically conductive paste for connecting thep-type thermoelectric material comprising: (i) at least one powderyoxide selected from the group consisting of a complex oxide representedby the formula Ca_(a)A¹ _(b)Co_(c)A² _(d)O_(e) wherein A¹ is one or moreelements selected from the group consisting of Na, K, Li, Ti, V, Cr, Mn,Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al, Bi, Y, and lanthanoids; A² is one ormore elements selected from the group consisting of Ti, V, Cr, Mn, Fe,Ni, Cu, Mo, W, Nb, and Ta; 2.2≦a≦3.6; 0≦b≦0.8; 2≦c≦4.5; 0 5≦d≦2; and8≦e≦10; and a complex oxide represented by the formula Bi_(f)Pb_(g)M¹_(h)Co_(i)M² _(j)O_(k) wherein M¹ is one or more elements selected fromthe group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb,Ca, Sr, Ba, Al, Y, and lanthanoids; M² is one or more elements selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, andTa; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; 1.6≦i≦2.2; 0≦j≦0.5; and 8≦k≦10; and(ii) at least one powdery electrically conductive metal selected fromthe group consisting of gold, silver, platinum, and alloys containing atleast one of these metals; and the electrically conductive paste forconnecting the n-type thermoelectric material comprising: (i) at leastone powdery oxide selected from the group consisting of a complex oxiderepresented by the formula Ln_(m)R¹ _(n)Ni_(p)R² _(q)O_(r) wherein Ln isone or more elements selected from the group consisting of lanthanoids;R¹ is one or more elements selected from the group consisting of Na, K,Sr, Ca, and Bi; R²is one or more elements selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, and Ta; 0.5≦m≦1.2;0≦n≦0.5; 0.5≦p≦1.2; 0≦q≦0.5; and 2.7≦r≦3.3; and a complex oxiderepresented by the formula (Ln_(s)R³ _(t))₂Ni_(u)R⁴ _(v)O_(w) wherein Lnis one or more elements selected from the group consisting oflanthanoids; R³ is one or more elements selected from the groupconsisting of Na, K, Sr, Ca, and Bi; R⁴is one or more elements selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, andTa; 0.5≦s≦1.2; 0≦t≦0.5; 0.5≦u≦1.2; 0≦v≦0.5; and 3.6≦r≦4.4; and (ii) atleast one powdery electrically conductive metal selected from the groupconsisting of gold, silver, platinum, and alloys containing at least oneof these metals.
 14. A thermoelectric element wherein one end of ap-type thermoelectric material and one end of an n-type thermoelectricmaterial are each connected to an electrically conductive substrate withan electrically conductive paste; the p-type thermoelectric materialcomprising a complex oxide represented by the formula Ca_(a)A¹_(b)Co₄O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; 2.2≦a≦3.6; 0≦b≦0.8; and 8≦e≦10; or a complexoxide represented by the formula Bi_(f)Pb_(g)M¹ _(h)Co₂O_(k) wherein M¹is one or more elements selected from the group consisting of Sr, Ca,and Ba; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10; the n-typethermoelectric material comprising a complex oxide represented by theformula La_(m)R¹ _(n)NiO_(r) wherein R¹ is one or more elements selectedfrom the group consisting of Na, K, Sr, Ca, and Bi; 0.5≦m≦1.2; 0≦n≦0.5;and 2.7≦r≦3.3; or a complex oxide represented by the formula (La_(s)R³_(t))₂NiO_(w) wherein R³ is one or more elements selected from the groupconsisting of Na, K, Sr, Ca, and Bi: 0.5≦s≦1.2; 0≦t≦0.5; and 3.6≦w≦4.4;the electrically conductive paste for connecting the p-typethermoelectric material to the electrically conductive substratecomprising (i) at least one powdery oxide selected from the groupconsisting of a complex oxide represented by the formula Ca_(a)A¹_(b)Co₄O_(e) wherein A¹ is one or more elements selected from the groupconsisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Ba, Al,Bi, Y, and lanthanoids; 2.2≦a≦3.6; 0≦b≦0.8; and 8≦e≦10; and a complexoxide represented by the formula Bi_(f)Pb_(g)M¹ _(h)Co₂O_(k) wherein M¹is one or more elements selected from the group consisting of Sr, Ca,and Ba; 1.8≦f≦2.2; 0≦g≦0.4; 1.8≦h≦2.2; and 8≦k≦10; and (ii) at least onepowdery electrically conductive metal selected from the group consistingof gold, silver, platinum, and alloys containing at least one of thesemetals; and the electrically conductive paste for connecting the n-typethermoelectric material to the electrically conductive substratecomprising (i) at least one powdery oxide selected from the groupconsisting of a complex oxide represented by the formula La_(m)R¹_(n)NiO_(r) wherein R¹ is one or more elements selected from the groupconsisting of Na, K, Sr, Ca, and Bi; 0.5≦m≦1.2; 0≦n≦0.5; and 2.7≦r≦3.3;and a complex oxide represented by the formula (La_(s)R³ _(t))₂NiO_(w)wherein R³ is one or more elements selected from the group consisting ofNa, K, Sr, Ca, and Bi: 0.5≦s≦1.2; 0≦t≦0.5; and 3.6≦w≦4.4; and (ii) atleast one powdery electrically conductive metal selected from the groupconsisting of gold, silver, platinum, and alloys containing at least oneof these metals.
 15. A thermoelectric module comprising a plurality ofthe thermoelectric elements of claim 12, wherein the thermoelectricelements are connected in series such that an unbonded end portion ofthe p-type thermoelectric material of one thermoelectric element isconnected to an unbonded end portion of the n-type thermoelectricmaterial of another thermoelectric element on a substrate.
 16. Athermoelectric conversion method comprising positioning one side of thethermoelectric module of claim 15 at a high-temperature environment andpositioning the other side of the module at a low-temperatureenvironment.
 17. A thermoelectric module comprising a plurality of thethermoelectric elements of claim 13, wherein the thermoelectric elementsare connected in series such that an unbonded end portion of a p-typethermoelectric material of one thermoelectric element is connected to anunbonded end portion of an n-type thermoelectric material of anotherthermoelectric element on a substrate.
 18. A thermoelectric conversionmethod comprising positioning one side of the thermoelectric module ofclaim 17 at a high-temperature environment and positioning the otherside of the module at a low-temperature environment.